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CK-12 Algebra - Basic 



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Gloag Gloag Kramer 



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Printed: April 5, 2012 



/lexbotK 

Nov? generation textbooks 




Authors 

Andrew Gloag, Anne Gloag, Melissa Kramer 



Editor 

Annamaria Farbizio 



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Contents 



1 Expressions, Equations, and 

Functions 1 

1.1 Variable Expressions 1 

1.2 Order of Operations 6 

1.3 Patterns and Expressions 11 

1.4 Equations and Inequalities 14 

1.5 Functions as Rules and Tables 19 

1.6 Functions as Graphs 25 

1.7 A Problem-Solving Plan 36 

1.8 Problem-Solving Strategies: Make a Table; Look for a Pattern 40 

1.9 Chapter 1 Review 44 

1.10 Chapter 1 Test 47 

2 Properties of Real Numbers 49 

2.1 Integers and Rational Numbers 49 

2.2 Addition of Rational Numbers 55 

2.3 Subtraction of Rational Numbers 59 

2.4 Multiplication of Rational Numbers 62 

2.5 The Distributive Property 67 

2.6 Division of Rational Numbers 70 

2.7 Square Roots and Real Numbers 73 

2.8 Problem-Solving Strategies: Guess and Check and Work Backwards 77 

2.9 Chapter 2 Review 80 

2.10 Chapter 2 Test 83 

3 Linear Equations 84 

3.1 One-Step Equations 85 

3.2 Two-Step Equations 89 

3.3 Multi-Step Equations 93 

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3.4 Equations with Variables on Both Sides 96 

3.5 Ratios and Proportions 99 

3.6 Scale and Indirect Measurement 103 

3.7 Percent Problems 108 

3.8 Problem-Solving Strategies: Use a Formula 113 

3.9 Chapter 3 Review 115 

3.10 Chapter 3 Test 117 

4 Graphing Linear Equations and 

Functions 119 

4.1 The Coordinate Plane 119 

4.2 Graphs of Linear Equations 125 

4.3 Graphs Using Intercepts 131 

4.4 Slope and Rate of Change 137 

4.5 Graphs Using Slope-Intercept Form 144 

4.6 Direct Variation 149 

4.7 Linear Function Graphs 154 

4.8 Problem-Solving Strategies: Read a Graph; Make a Graph 159 

4.9 Chapter 4 Review 163 

4.10 Chapter 4 Test 167 

5 Writing Linear Equations 169 

5.1 Linear Equations in Slope-Intercept Form 169 

5.2 Linear Equations in Point-Slope Form 177 

5.3 Linear Equations in Standard Form 182 

5.4 Equations of Parallel and Perpendicular Lines 186 

5.5 Fitting a Line to Data 192 

5.6 Predicting with Linear Models 201 

5.7 Problem-Solving Strategies: Use a Linear Model 207 

5.8 Problem-Solving Strategies: Dimensional Analysis 212 

5.9 Chapter 5 Review 215 

5.10 Chapter 5 Test 217 

6 Linear Inequalities and 
Absolute Value; An 

Introduction to Probability 219 

6.1 Inequalities Using Addition and Subtraction 219 

6.2 Inequalities Using Multiplication and Division 224 

6.3 Multi-Step Inequalities 227 

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6.4 Compound Inequalities 232 

6.5 Absolute Value Equations 238 

6.6 Absolute Value Inequalities 243 

6.7 Linear Inequalities in Two Variables 245 

6.8 Theoretical and Experimental Probability 253 

6.9 Chapter 6 Review 258 

6.10 Chapter 6 Test 260 

7 Systems of Equations and 

Inequalities; Counting Methods 262 

7.1 Linear Systems by Graphing 262 

7.2 Solving Systems by Substitution 268 

7.3 Solving Linear Systems by Addition or Subtraction 275 

7.4 Solving Linear Systems by Multiplication 278 

7.5 Special Types of Linear Systems 283 

7.6 Systems of Linear Inequalities 289 

7.7 Probability and Permutations 297 

7.8 Probability and Combinations 300 

7.9 Chapter 7 Review 303 

7.10 Chapter 7 Test 306 

8 Exponents and Exponential 

Functions 308 

8.1 Exponential Properties Involving Products 308 

8.2 Exponential Properties Involving Quotients 311 

8.3 Zero, Negative, and Fractional Exponents 314 

8.4 Scientific Notation 317 

8.5 Exponential Growth Functions 321 

8.6 Exponential Decay Functions 326 

8.7 Geometric Sequences and Exponential Functions 331 

8.8 Problem-Solving Strategies 334 

8.9 Chapter 8 Review 336 

8.10 Chapter 8 Test 338 

9 Polynomials and Factoring; 

More on Probability 339 

9.1 Addition and Subtraction of Polynomials 339 

9.2 Multiplication of Polynomials 345 

9.3 Special Products of Polynomials 350 

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9.4 Polynomial Equations in Factored Form 353 

9.5 Factoring Quadratic Expressions 358 

9.6 Factoring Special Products 362 

9.7 Factoring Polynomials Completely 365 

9.8 Probability of Compound Events 370 

9.9 Chapter 9 Review 373 

9.10 Chapter 9 Test 375 

10 Quadratic Equations and 

Functions 377 

10.1 Graphs of Quadratic Functions 377 

10.2 Solving Quadratic Equations by Graphing 385 

10.3 Solving Quadratic Equations Using Square Roots 391 

10.4 Solving Quadratic Equations by Completing the Square 394 

10.5 Solving Quadratic Equations Using the Quadratic Formula 399 

10.6 The Discriminant 403 

10.7 Linear, Exponential, and Quadratic Models 407 

10.8 Problem-Solving Strategies: Choose a Function Model 413 

10.9 Chapter 10 Review 417 

lO.lOChapter 10 Test 420 

11 Radicals and Geometry 

Connections; Data Analysis 422 

11.1 Graphs of Square Root Functions 422 

11.2 Radical Expressions 426 

11.3 Radical Equations 432 

11.4 The Pythagorean Theorem and its Converse 436 

11.5 The Distance and Midpoint Formulas 441 

11.6 Measures of Central Tendency and Dispersion 447 

11.7 Stem- and-Leaf Plots and Histograms 454 

11.8 Box-and- Whisker Plots 461 

11.9 Chapter 11 Review 467 

ll.lOChapter 11 Test 469 

12 Rational Equations and 

Functions; Statistics 471 

12.1 Inverse Variation Models 471 

12.2 Graphs of Rational Functions 474 

12.3 Division of Polynomials 480 

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12.4 Rational Expressions 483 

12.5 Multiplication and Division of Rational Expressions 487 

12.6 Addition and Subtraction of Rational Expressions 490 

12.7 Solution of Rational Equations 495 

12.8 Surveys and Samples 499 

12.9 Chapter 12 Review 509 

12.10Chapter 12 Test 511 



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Chapter 1 

Expressions, Equations, and 
Functions 



The study of expressions, equations, and functions is the basis of mathematics. Each mathematical subject 
requires knowledge of manipulating equations to solve for a variable. Careers such as automobile accident 
investigators, quality control engineers, and insurance originators use equations to determine the value of 
variables. 




Functions are methods of explaining relationships and can be represented as a rule, a graph, a table, or in 
words. The amount of money in a savings account, how many miles run in a year, or the number of trout 
in a pond are all described using functions. 

Throughout this chapter, you will learn how to choose the best variables to describe a situation, simplify 
an expression using the Order of Operations, describe functions in various ways, write equations, and solve 
problems using a systematic approach. 



1.1 Variable Expressions 

Who Speaks Math, Anyway? 



When someone is having trouble with algebra, they may say, "I don't speak math!" While this may seem 
weird to you, it is a true statement. Math, like English, French, Spanish, or Arabic, is a secondary language 
that you must learn in order to be successful. There are verbs and nouns in math, just like in any other 
language. In order to understand math, you must practice the language. 

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A verb is a "doing" word, such as running, jumps, or drives. In mathematics, verbs are also "doing" words. 
A math verb is called an operation. Operations can be something you have used before, such as addition, 
multiplication, subtraction, or division. They can also be much more complex like an exponent or square 
root. 

Example: Suppose you have a job earning $8.15 per hour. What could you use to quickly find out how 
much money you would earn for different hours of work? 

Solution: You could make a list of all the possible hours, but that would take forever! So instead, you let 
the "hours you work" be replaced with a symbol, like h for hours, and write an equation such as: 

amount of money = 8.15(h) 

A noun is usually described as a person, place, or thing. In mathematics, nouns are called numbers and 
variables. A variable is a symbol, usually an English letter, written to replace an unknown or changing 
quantity. 




Example: What variables would be choices for the following situations? 

a. the number of cars on a road 

b. time in minutes of a ball bounce 

c. distance from an object 

Solution: There are many options, but here are a few to think about. 

a. Cars is the changing value, so c is a good choice. 

b. Time is the changing value, so t is a good choice. 

c. Distance is the varying quantity, so d is a good choice. 



Why Do They Do That? 

Just like in the English language, mathematics uses several words to describe one thing. For example, 
sum, addition, more than, and plus all mean to add numbers together. The following definition shows an 
example of this. 

Definition: To evaluate means to follow the verbs in the math sentence. Evaluate can also be called 
simplify or answer. 

To begin to evaluate a mathematical expression, you must first substitute a number for the variable. 

Definition: To substitute means to replace the variable in the sentence with a value. 

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Now try out your new vocabulary. 

Example: EVALUATE 7y - 11, when y = 4. 

Solution: Evaluate means to follow the directions, which is to take 7 times y and subtract 11. Because y 
is the number 4, 



7x4-11 

28-11 

17 

The solution is 17. 



We have "substituted" the number 4 for y. 
Multiplying 7 and 4 
Subtracting 11 from 28 



Because algebra uses variables to represent the unknown quantities, the multiplication symbol x is often 
confused with the variable x. To help avoid confusion, mathematicians replace the multiplication symbol 
with parentheses ( ), the multiplication dot •, or by writing the expressions side by side. 

Example: Rewrite P = 2x/ + 2xw with alternative multiplication symbols. 

Solution: P = 2x/ + 2xw can be written as P = 2 • / + 2 • w 

It can also be written as P = 2/ + 2w. 

The following is a real-life example that shows the importance of evaluating a mathematical variable. 

Example: To prevent major accidents or injuries, these horses must be fenced in a rectangular pasture. If 
the dimensions of the pasture are 300 feet by 225 feet, how much fencing should the ranch hand purchase 
to enclose the pasture? 

Solution: Begin by drawing a diagram of the pasture and labeling what you know. 

w 




w 

To find the amount of fencing needed, you must add all the sides together; 



L + L+W+W. 



By substituting the dimensions of the pasture for the variables L and W, the expression becomes 



300 + 300 + 225 + 225. 



Now we must evaluate by adding the values together. The ranch hand must purchase 1,050 feet of fencing. 

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I 




Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Variable Expressions (12:26) In 1 - 4, write the expression in a more 




Figure 1.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/479 



condensed form by leaving out a multiplication symbol. 



1. 


2x11* 


2. 


1.35 -y 


3. 


3x± 


4. 


\'Z 



In 5 - 9, evaluate the expression. 

5. 5m + 7 when m = 3. 

6. h(c) when c = 63. 

7. $8.15(A) when h = 40. 

8. (it -11)-=- 8 when k = 43. 

9. Evaluate (-2) 2 + 3(j) when j = -3. 

In 10 - 17, evaluate the expressions. Let a = -3, b = 2, c = 5, and d = -4. 



10. 2a + 3b 
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11. 


Ac + d 


12. 


5ac - 2b 


13. 


2a 
c-d 


14. 


3b 
d 


15. 


a-4b 
3c+2d 


16. 


1 

a+b 


17. 


ab 



In 18 - 25, evaluate the expressions. Let x = -1, y = 2, z = -3, and w = 4. 

18. 8x 3 



19. 


5x 2 
6z 3 


20. 


3z 2 - 5w 2 


21. 


x 2 -y 2 

z 3 +w$ 
z 3 -w 3 


22. 


23. 


2x 2 - 3x 2 + 5x - 4 


24. 


4w 3 + 3w 2 - w + 2 


25. 


3 + ^ 



In 26 - 30, choose an appropriate variable to describe each situation. 

26. The number of hours you work in a week 

27. The distance you travel 

28. The height of an object over time 

29. The area of a square 

30. The number of steps you take in a minute 

In 31 - 35, underline the math verb(s) in the sentence. 

31. The product of six and v 

32. Four plus y minus six 

33. Sixteen squared 

34. U divided by 3 minus eight 

35. The square root of 225 

In 36-40, evaluate the real-life problems. 

36. The measurement around the widest part of these holiday bulbs is called their circumference. The 
formula for circumference is 2(r)n, where n « 3.14 and r is the radius of the circle. Suppose the radius 
is 1.25 inches. Find the circumference. 

37. The dimensions of a piece of notebook paper are 8.5 inches by 11 inches. Evaluate the writing area 
of the paper. The formula for area is length x width. 

38. Sonya purchases 16 cans of soda at $0.99 each. What is the amount Sonya spent on soda? 

39. Mia works at a job earning $4.75 per hour. How many hours should she work to earn $124.00? 

40. The area of a square is the side length squared. Evaluate the area of a square with side length 10.5 
miles. 

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Figure 1.2: Christmas Baubles by Petr Kratochvil 

1.2 Order of Operations 

The Mystery of Math Verbs 

Some math verbs are "stronger" than others and must be done first. This method is known as the Order 
of Operations. 

A mnemonic (a saying that helps you remember something difficult) for the Order of Operations is 
PEMDAS - Please Excuse My Daring Aunt Sophie. 

The Order of Operations: 

Whatever is found inside PARENTHESES must be done first. EXPONENTS are to be simplified 
next. MULTIPLICATION and DIVISION are equally important and must be performed moving left 
to right. ADDITION and SUBTRACTION are also equally important and must be performed moving 
left to right. 

Example 1: Use the Order of Operations to simplify (7-2)x4-i-2-3 

Solution: First, we check for parentheses. Yes, there they are and must be done first. 

(7-2)x4-2-3 = (5)x4-2-3 

Next we look for exponents (little numbers written a little above the others). No, there are no exponents 
so we skip to the next math verb. 

Multiplication and division are equally important and must be done from left to right. 

5x4-2-3= 20 -2-3 
20^2-3 = 10-3 

Finally, addition and subtraction are equally important and must be done from left to right. 

10 - 3 = 7 This is our answer. 

Example 2: Use the Order of Operations to simplify the following expressions. 

a) 3x5-7-2 

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b) 3 x (5 - 7) -f 2 

c) (3x5) -(7 -f 2) 
Solutions: 

a) There are no parentheses and no exponents. Go directly to multiplication and division from left to right: 
3x5-7-2 = 15-7-2 = 15-3.5 

Now subtract: 15 - 3.5 = 11.5 

b) Parentheses must be done first: 3 x (-2) -f 2 

There are no exponents, so multiplication and division come next and are done left to right: 3 x (-2) 4- 2 = 
-6 - 2 = -3 

c) Parentheses must be done first: (3 x 5) - (7 -f 2) = 15 - 3.5 

There are no exponents, multiplication, division, or addition, so simplify: 

15-3.5 = 11.5 

Parentheses are used two ways. The first is to alter the Order of Operations in a given expression, such as 
example (b). The second way is to clarify an expression, making it easier to understand. 

Some expressions contain no parentheses while others contain several sets of parentheses. Some expressions 
even have parentheses inside parentheses! When faced with nested parentheses, start at the innermost 
parentheses and work outward. 

Example 3: Use the Order of Operations to simplify 8 - [19 - (2 + 5) - 7] 

Solution: Begin with the innermost parentheses: 

8 - [19 - (2 + 5) - 7] = 8 - [19 - 7 - 7] 
Simplify according to the Order of Operations: 

8 - [19 - 7 - 7] = 8 - [5] = 3 

Evaluating Algebraic Expressions with Fraction Bars 

Fraction bars count as grouping symbols for PEMDAS, and should be treated as a set of parentheses. 
All numerators and all denominators can be treated as if they have invisible parentheses. When real 
parentheses are also present, remember that the innermost grouping symbols should be evaluated first. If, 
for example, parentheses appear on a numerator, they would take precedence over the fraction bar. If the 
parentheses appear outside of the fraction, then the fraction bar takes precedence. 

Example 4: Use the Order of Operations to simplify the following expressions. 

a) ^p - 1 when z = 2 

b) (f±f - l) + b when a = 3 and b = 1 

c ) 2 x I w ( ^2)2 - 1 ) when w = 11, x = 3, y = 1 and z = -2 

Solutions: Begin each expression by substituting the appropriate value for the variable: 
a) - 4 - - 1 = | - 1. Rewriting 1 as a fraction, the expression becomes: 

5 4 _ 1 

4 " 4 ~ 4 

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U ) (1+4) ~~ 5 — L 

(1 - 1) + b Substituting 1 for b, the expression becomes + 1 = 1 
c) 2 (Ill±gf|)»-l) = 2(<i«)-l) = 2(f-l) 

Continue simplifying: 2 (f - §) = 2 (§) = 2(1) = 2 

Using a Calculator to Evaluate Algebraic Expressions 

A calculator, especially a graphing calculator, is a very useful tool in evaluating algebraic expressions. The 
graphing calculator follows the Order of Operations, PEMDAS. In this section, we will explain two ways 
of evaluating expressions with the graphing calculator. 

Method #1: This method is the direct input method. After substituting all values for the variables, you 
type in the expression, symbol for symbol, into your calculator. 

Evaluate [3(x 2 - l) 2 - x 4 + 12] + 5x 3 - 1 when x = -3. 



(3((*5)*-l)»-(-J) A 4M 
2>*5< -3> A 3-i 

-13 



Substitute the value x = -3 into the expression. 

[3((-3) 2 - l) 2 - (-3) 4 + 12] + 5(-3) 3 - 1 

The potential error here is that you may forget a sign or a set of parentheses, especially if the expression 
is long or complicated. Make sure you check your input before writing your answer. An alternative is to 
type the expression in by appropriate chunks - do one set of parentheses, then another, and so on. 

Method #2: This method uses the STORE function of the Texas Instrument graphing calculators, such 
as the TI-83, TI-84, or TI-84 Plus. 

First, store the value x = -3 in the calculator. Type -3 [STO] x. {The letter x can be entered using 
the x-[VAR] button or [ALPHA] + [STO]). Then type in the expression in the calculator and press 
[ENTER]. 



•3*x 

<3<x*-l>*-x*4*l2>*3 x 

-!3 



The answer is -13. 

Note: On graphing calculators there is a difference between the minus sign and the negative sign. When we 
stored the value negative three, we needed to use the negative sign, which is to the left of the [ENTER] 
button on the calculator. On the other hand, to perform the subtraction operation in the expression we 
used the minus sign. The minus sign is right above the plus sign on the right. 

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You can also use a graphing calculator to evaluate expressions with more than one variable. 

3x 2 -4y 2 +x 4 



Evaluate the expression: — — — ~[ x for x = -2, y 



1. 



<3 x*-4V«*x^4>/Cx*V>J 

*. 888888888383 



Store the values of x and y. -2 [STO] x 1 1 [STO] y. The letters x and y can be entered using [ALPHA] + 
[KEY]. Input the expression in the calculator. When an expression shows the division of two expressions 
be sure to use parentheses: (numerator) -f (denominator). Press [ENTER] to obtain the answer —.88 or 

_8 
9" 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Order of Operations (14:23) 




Figure 1.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/708 

Use the Order of Operations to simplify the following expressions. 

1. 8 -(19 -(2 + 5) -7) 

2. 2 + 7x11-12 -=-3 

3. (3 + 7) -=-(7-12) 

4 2-(3+(2-l)) (0 ~x 
4 ' 4-(6+2) ^ °J 

5. 8-5 + 6 2 

6. 9-3x7- 2 3 + 7 

7. 8 + 12-6 + 6 

8. (7 2 -3 2 )-8 



Evaluate the following expressions involving variables. 



jk 



9- tt£ when j = 6 and k 
10. 2y 2 when x = 1 and y 



12. 

5 



9 



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11. 3x 2 + 2x + 1 when x = 5 

12. (y 2 - x) 2 when x = 2 and y = 1 

Evaluate the following expressions involving variables. 

13. n o 4 * n when x = 2 

2 2 

14. ^ + ^ when x = 1, y = -2, and z = 4. 

15. aj^ when x = 3, y = 2, and z = 5 

2 2 

16. — hrr — v when x = -1 and z = 3 

xz-2x(z-x) 

The formula to find the volume of a square pyramid is V = — 3 • Evaluate the volume for the given values. 

17. s = 4 inches, h = 18 inches 

18. 5= 10 feet,h = 50 /eef 

19. h = 7 meters, s = 12 meters 

20. /*= 27 feet, s= 13 /eef 

21. S = 16 cm, ft = 90 cm 

In 22-25, insert parentheses in each expression to make a true equation. 

22. 5-2-6-4 + 2 = 5 

23. 12^4 + 10-3-3 + 7= 11 

24. 22 - 32 - 5 • 3 - 6 = 30 

25. 12-8-4-5 = -8 

In 26 - 29, evaluate each expression using a graphing calculator. 

26. x 2 + 2x - xy when x = 250 and y = -120 

27. (xy - y 4 ) 2 when x = 0.02 and y = -0.025 

28. ^g^_ whenx=^, y=|,andz = -l 

29. 4^2 _ 2 wnen * = 3 and y = -hd 

30. The formula to find the volume of a spherical object (like a ball) is V = |(7r)r 3 , where r = the radius 
of the sphere. Determine the volume for a grapefruit with a radius of 9 cm. 

Mixed Review 

31. Let x = — 1. Find the value of -9x + 2. 

32. The area of a trapezoid is given by the equation A = |(<z + b). Find the area of a trapezoid with 
bases a = 10 cm,b = 15 cm^ and height h = 8 cm. 



ZI 



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33. The area of a circle is given by the formula A = nr 2 . Find the area of a circle with radius r = 17 
inches. 




1.3 Patterns and Expressions 

In mathematics, especially in algebra, we look for patterns in the numbers that we see. Using mathematical 
verbs and variables studied in lessons 1.1 and 1.2, expressions can be written to describe a pattern. 

Definition: An algebraic expression is a mathematical phrase combining numbers and/or variables 
using mathematical operations. 




Consider a theme park charging an admission of $28 per person. A rule can be written to describe the 
relationship between the amount of money taken at the ticket booth and the number of people entering 
the park. In words, the relationship can be stated as "The money taken in dollars is (equals) twenty-eight 
times the number of people who enter the park" 

The English phrase above can be translated (written in another language) into an algebraic expression. 
Using mathematical verbs and nouns learned from previous lessons, any sentence can be written as an 
algebraic expression. 

Example 1: Write an algebraic expression for the following phrase. 

The product of c and 4- 

Solution: The verb is product, meaning "to multiply." Therefore, the phrase is asking for the answer found 
by multiplying c and 4. The nouns are the number 4 and the variable c. The expression becomes 4xc, 4(c), 
or using shorthand, 4c. 

Example 2: Write an expression to describe the amount of revenue of the theme park. 

Solution: An appropriate variable to describe the number of people could be p. Rewriting the English 
phrase into a mathematical phrase, it becomes 28 x p. 

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Using Words to Describe Patterns 

Sometimes patterns are given in tabular format (meaning presented in a table). An important job of 
analysts is to describe a pattern so others can understand it. 

Example 3: Using the table below, describe the pattern in words. 



X 


-l 





1 


2 


3 


4 


y 


-5 





5 


10 


15 


20 



Solution: We can see from the table that y is five times bigger than x. Therefore, the pattern is that the 
u y value is five times larger than the x value." 

Example 4: Using the table below, describe the pattern in words and in an expression. 

Zarina has a $100 gift card and has been spending money in small regular amounts. She checks the balance 
on the card weekly, and records the balance in the following table. 

Table 1.1: 

Week # Balance ($) 

1 100 

2 78 

3 56 

4 34 

Solution: Each week the amount of her gift card is $22 less than the week before. The pattern in words 
is: "The gift card started at $100 and is decreasing by $22 each week." 

The expression found in example 4 can be used to answer many situations. Suppose, for instance, that 
Zarina has been using her gift card for 4 weeks. By substituting the number 4 for the variable w, it can be 
determined that Zarina has $12 left on her gift card. 

Solution: 

100 - 22w 



When w = 4, the expression becomes 



100-22(4) 
100 - 88 
12 

After 4 weeks, Zarina has $12 left on her gift card. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Patterns and Equations (13:18) 

www.ckl2.org 12 




Figure 1.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/709 

For exercises 1 - 15, translate the English phrase into an algebraic expression. For the exercises without a 
stated variable, choose a letter to represent the unknown quantity. 

1. Sixteen more than a number 

2. The quotient of h and 8 

3. Forty-two less than y 

4. The product of k and three 

5. The sum of g and -7 

6. r minus 5.8 

7. 6 more than 5 times a number 

8. 6 divided by a number minus 12 

9. A number divided by -11 

10. 27 less than a number times four 

11. The quotient of 9.6 and m 

12. 2 less than 10 times a number 

13. The quotient of d and five times s 

14. 35 less than x 

15. The product of 6, -9, and u 

In exercises 16 - 24, write an English phrase for each algebraic expression 



16. 


J-9 


17. 
18. 


n 
14 

17 -a 


19. 


3/ -16 


20. 
21. 
22. 


\{h){b) 

k. J_ z 

4.7-2/ 


23. 


5.8 + k 


24. 


2/ + 2w 



In exercises 25 - 28, define a variable to represent the unknown quantity and write an expression to describe 
the situation. 

25. The unit cost represents the quotient of the total cost and number of items purchased. Write an 
expression to represent the unit cost of the following: The total cost is $14.50 for n objects. 

26. The area of a square is the side length squared. 

27. The total length of ribbon needed to make dance outfits is 15 times the number of outfits. 



13 



www.ckl2.org 



28. What is the remaining amount of chocolate squares if you started with 16 and have eaten some? 

29. Describe a real- world situation that can be represented by h + 9. 

30. What is the difference between ^ and y? 

In questions 31 - 34, write the pattern of the table: a) in words and b) with an algebraic expression. 

31. Number of workers and number of video games packaged 



People 





1 


2 


5 


10 


50 


200 


Amount 





65 


87 


109 


131 


153 


175 



32. The number of hours worked and the total pay 





1 


2 


3 


4 


5 


6 


Pay 


15 


22 


29 


36 


43 


50 



33. The number of hours of an experiment and the total number of bacteria 



Hours 





1 


2 


5 


10 


Bacteria 





2 


4 


32 


1024 



34. With each filled seat, the number of people on a Ferris wheel doubles. 

(a) Write an expression to describe this situation. 

(b) How many people are on a Ferris wheel with 17 seats filled? 

35. Using the theme park situation from the lesson, how much revenue would be generated by 2,518 
people? 

Mixed Review 

36. Use parentheses to make the equation true: 10 + 6^-2-3 = 5. 

37. Find the value of 5x 2 - 4y for x = -4 and y = 5. 

38. Find the value of i y 2 for x = 2 and y = -4. 

x 6 +y z J 

39. Simplify: 2 - (t - 7) 2 x (u 3 - v) when t = 19, u = 4, and v = 2. 

40. Simplify: 2 - (19 - 7) 2 x (4 3 - 2). 

1.4 Equations and Inequalities 

When an algebraic expression is set equal to another value, variable, or expression, a new mathematical 
sentence is created. This sentence is called an equation. 

Definition: An algebraic equation is a mathematical sentence connecting an expression to a value, a 
variable, or another expression with an equal sign (=). 

Consider the theme park situation from lesson 1.3. Suppose there is a concession stand selling burgers 
and French fries. Each burger costs $2.50 and each order of French fries costs $1.75. You and your family 
will spend exactly $25.00 on food. How many burgers can be purchased? How many orders of fries? How 
many of each type can be purchased if your family plans to buy a combination of burgers and fries? 

www.ckl2.org 14 




The underlined word exactly lends a clue to the type of mathematical sentence you will need to write to 
model this situation. 

These words can be used to symbolize the equal sign: 

Exactly, equivalent, the same as, identical, is 

The word exactly is synonymous with equal, so this word is directing us to write an equation. Using the 
methods learned in lessons 1.2 and 1.3, read every word in the sentence and translate each into mathematical 
symbols. 

Example 1: Your family is planning to purchase only burgers. How many can be purchased with $25.00? 

Solution: 

Step 1: Choose a variable to represent the unknown quantity, say b for burgers. 

Step 2: Write an equation to represent the situation: 2.50/? = 25.00. 

Step 3: Think. What number multiplied by 2.50 equals 25.00? 

The solution is 10, so your family can purchase exactly ten burgers. 

Example 2: Translate the following into equations: 

a) 9 less than twice a number is 33. 

b) Five more than four times a number is 21. 

c) $20.00 was one-quarter of the money spent on pizza. 
Solutions: 

a) Let "a number" be n. So, twice a number is 2n. 
Nine less than that is 2n - 9. 

The word is means the equal sign, so 2n - 9 = 33. 

b) Let "a number" be x. So five more than four times a number is 21 can be written as: 4x + 5 = 21. 

c) Let "of the money" be m. The equation could be written as \m = 20.00. 

Definition: The solution to an equation or inequality is the value (or multiple values) that make the 
equation or inequality true. 

Using statement (c) from example 2, find the solution. 



15 www.ckl2.org 




-m = 20.00 
4 

Think: One-quarter can also be thought of as divide by four. What divided by 4 equals 20.00? 

The solution is 80. So, the money spent on pizza was $80.00. 

Checking an answer to an equation is almost as important as the equation itself. By substituting the value 
for the variable, you are making sure both sides of the equation balance. 

Example 3: Check that x = 5 is the solution to the equation 3x + 2 = -2x + 27. 

Solution: To check that x = 5 is the solution to the equation, substitute the value of 5 for the variable, x: 

3x + 2 = -2x + 27 

3. x + 2 = -2-x + 27 
3-5 + 2 = -2-5 + 27 
15 + 2 = -10 + 27 
17= 17 



Because 17 = 17 is a true statement, we can conclude that x = 5 is a solution to 3x + 2 
Example 4: Is z = 3 a solution to z 2 + 2z = 8? 
Solution: Begin by substituting the value of 3 for z. 

3 2 + 2(3) = 8 

9 + 6 = 8 

15 = 8 



-2jc + 27. 



Because 15 = 8 is NOT a true statement, we can conclude that z = 3 is not a solution to z 2 + 2z = 8. 



Sometimes Things Are Not Equal 

In some cases there are multiple answers to a problem or the situation requires something that is not 
exactly equal to another value. When a mathematical sentence involves something other than an equal 
sign, an inequality is formed. 

Definition: An algebraic inequality is a mathematical sentence connecting an expression to a value, a 
variable, or another expression with an inequality sign. 

Listed below are the most common inequality signs. 



www.ckl2.org 



16 



> "greater than" 

> "greater than or equal to" 

< "less than or equal to" 

< "less than" 

=£ "not equal to" 

Below are several examples of inequalities. 

3x<5 jc 2 + 2jc - 1 > -4- > - - 3 4-x<2x 

4 2 

Example 5: Translate the following into an inequality: Avocados cost $1.59 per pound. How many pounds 
of avocados can be purchased for less than $7.00? 

Solution: Choose a variable to represent the number of pounds of avocados purchased, say a. 

1.59(a) < 7 

You will be asked to solve this inequality in the exercises 




Checking the Solution to an Inequality 

Unlike equations, inequalities typically have more than one solution. Checking solutions to inequalities is 
more complex than checking solutions to equations. The key to checking a solution to an inequality is to 
choose a number that occurs within the solution set. 

Example 6: Check that m < 10 is a solution to 4m + 30 < 70. 

Solution: If the solution set is true, any value less than or equal to 10 should make the original inequality 
true. 

Choose a value less than 10, say 4. Substitute this value for the variable m. 

4(4) + 30 
16 + 30 
46<70 

The value found when m = 4 is less than 70. Therefore, the solution set is true. 

Why was the value 10 not chosen? Endpoints are not chosen when checking an inequality because the 
direction of the inequality needs to be tested. Special care needs to be taken when checking the solutions 
to an inequality. 

17 www.ckl2.org 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Equations and Inequalities (16:11) 




Figure 1.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/712 



1. Define solution. 

2. What is the difference between an algebraic equation and an algebraic inequality? Give an example 
of each. 

3. What are the five most common inequality symbols? 

In 4 - 11, define the variables and translate the following statements into algebraic equations. 

4. Peter's Lawn Mowing Service charges $10 per job and $0.20 per square yard. Peter earns $25 for a 
job. 

5. Renting the ice-skating rink for a birthday party costs $200 plus $4 per person. The rental costs 
$324 in total. 

6. Renting a car costs $55 per day plus $0.45 per mile. The cost of the rental is $100. 

7. Nadia gave Peter 4 more blocks than he already had. He already had 7 blocks. 

8. A bus can seat 65 passengers or fewer. 

9. The sum of two consecutive integers is less than 54. 

10. An amount of money is invested at 5% annual interest. The interest earned at the end of the year is 
greater than or equal to $250. 

11. You buy hamburgers at a fast food restaurant. A hamburger costs $0.49. You have at most $3 to 
spend. Write an inequality for the number of hamburgers you can buy. 

In 12 - 15, check that the given number is a solution to the corresponding equation. 

12. a = -3; 4a + 3 = -9 

-LO. X 77 , tX — r* 7J 77 

14. y = 2; 2.5y - 10.0 = -5.0 

15. z = -5; 2(5 - 2 Z ) = 20 - 2(z - 1) 

For exercises 16 - 19, check that the given number is a solution to the corresponding inequality. 



16. x= 12; 2(x + 6) < 8x 
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18 



17. z = -9; 1.4z + 5.2>0.4z 

18. y = 40; -\y+\ <-18 

19. ^ = 0.4; 80 > 10(3* + 2) 

In 20 - 24, find the value of the variable. 

20. m + 3 = 10 

21. 6x£ = 96 

22. 9-f= 1 

23. 8/z = 808 

24. a + 348 = 

25. Using the burger and French fries situation from the lesson, give three combinations of burgers and 
fries your family can buy without spending more than $25.00. 

26. Solve the avocado inequality from Example 5 and check your solution. 

27. You are having a party and are making sliders. Each person will eat 5 sliders. There will be seven 
people at your party. How many sliders do you need to make? 

28. The cost of a Ford Focus is 27% of the price of a Lexus GS 450h. If the price of the Ford is $15,000, 
what is the price of the Lexus? 

29. On your new job you can be paid in one of two ways. You can either be paid $1000 per month plus 
6% commission on total sales or be paid $1200 per month plus 5% commission on sales over $2000. 
For what amount of sales is the first option better than the second option? Assume there are always 
sales over $2000. 

30. Suppose your family will purchase only orders of French fries using the information found in the 
opener of this lesson. How many orders of fries can be purchased for $25.00? 

Mixed Review 

31. Translate into an algebraic equation: 17 less than a number is 65. 

32. Simplify the expression: 3 4 -f (9 x 3) + 6 - 2. 

33. Rewrite the following without the multiplication sign: A = | • b • h. 

34. The volume of a box without a lid is given by the formula V = 4x(10 - x) 2 , where lis a length in 
inches and V is the volume in cubic inches. What is the volume of the box when x = 2? 

1.5 Functions as Rules and Tables 

Instead of purchasing a one-day ticket to the theme park, Joseph decided to pay by ride. Each ride costs 
$2.00. To describe the amount of money Joseph will spend, several mathematical concepts can be used. 




19 www.ckl2.org 



First, an expression can be written to describe the relationship between the cost per ride and the number 
of rides, r. An equation can also be written if the total amount he wants to spend is known. An inequality 
can be used if Joseph wanted to spend less than a certain amount. 

Example 1: Using Joseph's situation, write the following: 

a. An expression representing his total amount spent 

b. An equation that shows Joseph wants to spend exactly $22.00 on rides 

c. An inequality that describes the fact that Joseph will not spend more than $26.00 on rides 
Solution: The variable in this situation is the number of rides Joseph will pay for. Call this r. 

a. 2(r) 

b. 2(r) = 22 

c. 2(r) < 26 

In addition to an expression, equation, or inequality, Joseph's situation can be expressed in the form of a 
function or a table. 

Definition: A function is a relationship between two variables such that the input value has ONLY one 
output value. 

Writing Equations as Functions 

A function is a set of ordered pairs in which the first coordinate, usually jc, matches with exactly one second 
coordinate, y. Equations that follow this definition can be written in function notation. The y coordinate 
represents the dependent variable, meaning the values of this variable depend upon what is substituted 
for the other variable. 

Consider Joseph's equation m = 2r. Using function notation, the value of the equation (the money spent 
m) is replaced with f(r). f represents the function name and (r) represents the variable. In this case the 
parentheses do not mean multiplication; they separate the function name from the independent variable. 

input 

i 

f(x) = y <— output 

function 
box 

Example 2: Rewrite the following equations in function notation. 

a. y = 7x - 3 

b. d = 65t 

c. F = 1.8C + 32 
Solution: 

a. According to the definition of a function, y = /(jc), so /(jc) = 7x - 3. 

b. This time the dependent variable is d. Function notation replaces the dependent variable, so d = f{t) = 
65^. 

c. F = /(C) = 1.8C + 32 

www.ckl2.org 20 



Why Use Function Notation? 

Why is it necessary to use function notation? The necessity stems from using multiple equations. Function 
notation allows one to easily decipher between the equations. Suppose Joseph, Lacy, Kevin, and Alfred 
all went to the theme park together and chose to pay $2.00 for each ride. Each person would have the 
same equation m = 2r. Without asking each friend, we could not tell which equation belonged to whom. 
By substituting function notation for the dependent variable, it is easy to tell which function belongs to 
whom. By using function notation, it will be much easier to graph multiple lines (Chapter 4). 

Example 3: Write functions to represent the total each friend spent at the park. 

Solution: J(r) = 2r represents Joseph's total, L(r) = 2r represents Lacy's total, K(r) = 2r represents 
Kevin's total, and A(r) = 2r represents Alfred's total. 

Using a Function to Generate a Table 

A function really is an equation. Therefore, a table of values can be created by choosing values to represent 
the independent variable. The answers to each substitution represent f(x). 

Use Joseph's function to generate a table of values. Because the variable represents the number of rides 
Joseph will pay for, negative values do not make sense and are not included in the value of the independent 
variable. 

Table 1.2: 

R J(r) = 2r 

2(0) = 

1 2(1) = 2 

2 2(2) =4 

3 2(3) = 6 

4 2(4) = 8 

5 2(5) = 10 

6 2(6) = 12 



As you can see, the list cannot include every possibility. A table allows for precise organization of data. 
It also provides an easy reference for looking up data and offers a set of coordinate points that can be 
plotted to create a graphical representation of the function. A table does have limitations; namely it cannot 
represent infinite amounts of data and it does not always show the possibility of fractional values for the 
independent variable. 



Domain and Range of a Function 

The set of all possible input values for the independent variable is called the domain. The domain can be 
expressed in words, as a set, or as an inequality. The values resulting from the substitution of the domain 
represent the range of a function. 

The domain of Joseph's situation will not include negative numbers because it does not make sense to ride 
negative rides. He also cannot ride a fraction of a ride, so decimals and fractional values do not make sense 
as input values. Therefore, the values of the independent variable r will be whole numbers beginning at 
zero. 

21 www.ckl2.org 



Domain: All whole numbers 

The values resulting from the substitution of whole numbers are whole numbers times two. Therefore, the 
range of Joseph's situation is still whole numbers just twice as large. 

Range: All even whole numbers 

Example 4: A tennis ball is bounced from a height and bounces back to 75% of its previous height. Write 
its function and determine its domain and range. 

Solution: The function of this situation is h(b) = 0.75/?, where b represents the previous bounce height. 

Domain: The previous bounce height can be any positive number, so b > 0. 

Range: The new height is 75% of the previous height, and therefore will also be any positive number 
(decimal or whole number), so the range is all positive real numbers. 

Multimedia Link For another look at the domain of a function, see the following video where the 
narrator solves a sample problem from the California Standards Test about finding the domain of an 
unusual function. Khan Academy CA Algebra I Functions (6:34) 




Figure 1.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/88 



Write a Function Rule 

In many situations, data is collected by conducting a survey or an experiment. To visualize the data, it is 
arranged into a table. Most often, a function rule is needed to predict additional values of the independent 
variable. 

Example 5: Write a function rule for the table. 



Number of CDs 
Cost ($) 



2 

24 



4 

48 



6 

72 



96 



10 
120 




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22 



Solution: You pay $24 for 2 CDs, 

$12. 



for 4 CDs, and $120 for 10 CDs. That means that each CD costs 



We can write the function rule. 

Cost = $12 x number of CDs or f(x) = 12* 

Example 6: Write a function rule for the table. 



X 


-3 


-2 


-1 





1 


2 


3 


y 


3 


2 


1 





1 


2 


3 



Solution: The values of the dependent variable are always the positive outcomes of the input values. This 
relationship has a special name, the absolute value. The function rule looks like this: f{x) = \x\. 

Represent a Real- World Situation with a Function 

Let's look at a real- world situation that can be represented by a function. 

Example 7: Maya has an internet service that currently has a monthly access fee of $11.95 and a 
connection fee of $0.50 per hour. Represent her monthly cost as a function of connection time. 

Solution: Let x = the number of hours Maya spends on the internet in one month and let y = Maya's 
monthly cost. The monthly fee is $11.95 with an hourly charge of $0.50. 

The total cost = flat fee + hourly fee x number of hours. The function is y = f(x) = 11.95 + 0.50x 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Domain and Range of a Function (12:52) 




Figure 1.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/454 



1. Rewrite using function notation: y = |x - 2. 

2. What is one benefit of using function notation? 

3. Define domain. 

4. True or false? Range is the set of all possible inputs for the independent variable. 

5. Generate a table from -5 < x < 5 for f(x) = ~{x) 2 - 2 

6. Use the following situation for question 6: Sheri is saving for her first car. She currently has $515.85 
and is savings $62 each week. 



23 



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(a) Write a function rule for the situation. 

(b) Can the domain be "all real numbers"? Explain your thinking. 

(c) How many weeks would it take Sheri to save $1,795.00? 

In 7 - 11, identify the domain and range of the function. 

7. Dustin charges $10 per hour for mowing lawns. 

8. Maria charges $25 per hour for math tutoring, with a minimum charge of $15. 

9. f(x) = 15jc-12 

10. f(x) = 2x 2 + 5 

11. /(*) = \ 

12. What is the range of the function y = x 2 - 5 when the domain is -2, -1, 0, 1, 2? 

13. What is the range of the function y = 2x - | when the domain is -2.5, 1.5, 5? 

14. Angie makes $6.50 per hour working as a cashier at the grocery store. Make a table of values that 
shows her earning for the input values 5, 10, 15, 20, 25, 30. 

15. The area of a triangle is given by: A = -^bh. If the base of the triangle is 8 centimeters, make a table 
of values that shows the area of the triangle for heights 1, 2, 3, 4, 5, and 6 centimeters. 

16. Make a table of values for the function f(x) = ^2x + 3 for the input values -1, 0, 1, 2, 3, 4, 5. 

17. Write a function rule for the table. 



x 

y 



3 

9 



4 
16 



5 
25 



6 
36 



18. Write a function rule for the table. 



hours 
cost 




15 



1 
20 



2 

25 



3 
30 



19. Write a function rule for the table. 



x 

y 



o 

24 



1 
12 



2 

6 



3 
3 



20. Write a function that represents the number of cuts you need to cut a ribbon in x number of pieces. 

21. Solomon charges a $40 flat rate and $25 per hour to repair a leaky pipe. Write a function that 
represents the total fee charged as a function of hours worked. How much does Solomon earn for a 
three-hour job? 

22. Rochelle has invested $2500 in a jewelry making kit. She makes bracelets that she can sell for $12.50 
each. How many bracelets does Rochelle need to make before she breaks even? 

23. Make up a situation in which the domain is all real numbers but the range is all whole numbers. 

Mixed Review 

24. Compare the following numbers 23 21.999. 

25. Write an equation to represent the following: the quotient of 96 and 4 is g. 

26. Write an inequality to represent the following: 11 minus b is at least 77. 

27. Find the value of the variable k : 13(h) = 169. 



www.ckl2.org 



24 



Quick Quiz 

1. Write a function rule to describe the following table: 



# of Books 


1 


2 


3 


4 


5 


6 


Cost 


4.75 


5.25 


5.75 


6.25 


6.75 


7.25 



2. Simplify: 84 - [(18 - 16) X 3]. 

3. Evaluate the expression |(y + 6) when y = 3. 

4. Rewrite using function notation: y = jx 2 . 

5. You purchased six video games for $29.99 each and three DVD movies for $22.99. What is the total 
amount of money you spent? 



1.6 Functions as Graphs 



Once a table has been created for a function, the next step is to visualize the relationship by graphing 
the coordinates (independent value, dependent value). In previous courses, you have learned how to plot 
ordered pairs on a coordinate plane. The first coordinate represents the horizontal distance from the origin 
(the point where the axes intersect). The second coordinate represents the vertical distance from the origin. 



— fx- 

E==E=E=E±d-H-H-==EE 

1 ' 



To graph a coordinate point such as (4,2) we start at the origin. 

Because the first coordinate is positive four, we move 4 units to the right. 

From this location, since the second coordinate is positive two, we move 2 units up. 



















J 


J 






















°: 






















































































































































• 






































p 


' -6 -5 -4 -3 -2 -1 , 


Si 2 3 4 5 6 


r r 






. . _2- 


































on 


y |: 




























































p; 




































































ft- 

































,n 


i* 










































































































































































a-- 


r -6 -5 -4 -3 -; 


1 


1 


> \\ 4 


! 5 6 


' a 






























































































































G 










































-I — I — I — Lft- 





















S : 






















































































I 


























I 




(4 


2. 1 
























__._... 


. 


. 
















B- 


r-6-s 


\ ■■ 


1 


>-1 


,12 3 4 5 


^ " 


' 


! 
































































<\ 




























































a 


■ 










































-8 













Example 1: Plot the following coordinate points on the Cartesian plane. 

(a) (5, 3) 

(b) (-2, 6) 



25 



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(c) (3, -4) 

(d) (-5, -7) 

Solution: We show all the coordinate points on the same plot. 











8- 


























{-2,6) ■ 
































U 


































A 












































(G 


3) 






















































£.' 


























8 -7 -6 -\ 


i -4 -3 -2-1 . 


.1 2 


4 5 6 7 I 


! 




2 


















































(3-4) 






















° 


























- 


















ill 




7) 


4,. 


I I 















Notice that: 

For a positive x value we move to the right. 

For a negative x value we move to the left. 

For a positive y value we move up. 

For a negative y value we move down. 

When referring to a coordinate plane, also called a Cartesian plane, the four sections are called quadrants. 
The first quadrant is the upper right section, the second quadrant is the upper left, the third quadrant is 
the lower left and the fourth quadrant is the lower right. 

+Y 













- i 


t 




















3 


















ii 




-) 






1 




























x- 






















-4 


■: 




■ 








■ 


i h 
































ii 




■■/ 






V 






































1 


' 











■V 



Suppose we wanted to visualize Joseph's total cost of riding at the amusement park. Using the table 
generated in Lesson 1.5, the graph can be constructed as (number of rides, total cost). 

Table 1.3: 



J(r) = 2r 




1 
2 
3 
4 
5 
6 



2(0) = 
2(1) = 2 
2(2) =4 
2(3) = 6 
2(4) = 8 
2(5) = 10 
2(6) = 12 



www.ckl2.org 



26 



o ° 



2 5_ 


/ 


Joseph's Total Cost 


















I2 U 














1 P 






























iri- 






















1 


W 








































7 R- 








IP 
























1 


; 












i 


I 












1 


r^ 




















rj - 






i 












i 


i 












' 


F 






















9 c; - 




i 












j 


i 












^ 


I 
































01 


£ — 











2 3 4 

Number of Rides 



The green dots represent the combination of (r, J(r)). The dots are not connected because the domain of 
this function is all whole numbers. By connecting the points we are indicating that all values between the 
ordered pairs are also solutions to this function. Can Joseph ride 2^ rides? Of course not! Therefore, we 
leave this situation as a scatter plot. 

Example 2: Graph the function that has the following table of values. 



Side of the Square 
Area of the Square 








2 

4 



4 
16 



Solution: The table gives us five sets of coordinate points: 

(0, 0), (1, 1), (2, 4), (3, 9), (4, 16). 

To graph the function, we plot all the coordinate points. Because the length of a square can be fractional 
values, but not negative, the domain of this function is all positive real numbers, or x > 0. This means 
the ordered pairs can be connected with a smooth curve. This curve will continue forever in the positive 
direction, shown by an arrow. 



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side of square 



side of square 



Writing a Function Rule Using a Graph 

In many cases, you are given a graph and asked to determine its function. From a graph, you can read pairs 
of coordinate points that are on the curve of the function. The coordinate points give values of dependent 



27 



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and independent variables. These variables are related to each other by a rule. It is important we make 
sure this rule works for all the points on the curve. 

In this course, you will learn to recognize different kinds of functions. There will be specific methods that 
you can use for each type of function that will help you find the function rule. For now, we will look at 
some basic examples and find patterns that will help us figure out the relationship between the dependent 
and independent variables. 

Example 3: The graph below shows the distance that an inchworm covers over time. Find the function 
rule that shows how distance and time are related to each other. 



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<D 




















4 
















t3 


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-2 


































i 






1 






L 



2 4 6 

time (seconds) 



Solution: Make table of values of several coordinate points to identify a pattern. 



Time 





1 


2 


3 


4 


5 


6 


Distance 





1.5 


3 


4.5 


6 


7.5 


9 



We can see that for every minute the distance increases by 1.5 feet. We can write the function rule as: 

Distance = 1.5 x time 

The equation of the function is f{x) = 1.5x 



Analyze the Graph of a Real- World Situation 

Graphs are used to represent data in all areas of life. You can find graphs in newspapers, political cam- 
paigns, science journals, and business presentations. 

Here is an example of a graph you might see reported in the news. Most mainstream scientists believe 
that increased emissions of greenhouse gases, particularly carbon dioxide, are contributing to the warming 
of the planet. The graph below illustrates how carbon dioxide levels have increased as the world has 
industrialized. 



www.ckl2.org 



28 



Global concentration of Co2 in the atmosphere 

Parts per million (ppm) 

380- 



360 

340 
320 
300 
2S0 



260 



















































^ 


























V 



















































































1870 



1890 



1910 



1930 



1950 



1970 1990 
SOURCE: UNEP 



From this graph, we can find the concentration of carbon dioxide found in the atmosphere in different 
years. 

1900 - 285 parts per million 

1930 - 300 parts per million 

1950 - 310 parts per million 

1990 - 350 parts per million 

In Chapter 9, you will learn how to approximate an equation to fit this data using a graphing calculator. 



Determining Whether a Relation Is a Function 



You saw that a function is a relation between the independent and the dependent variables. It is a rule 
that uses the values of the independent variable to give the values of the dependent variable. A function 
rule can be expressed in words, as an equation, as a table of values, and as a graph. All representations 
are useful and necessary in understanding the relation between the variables. 

Definition: A relation is a set of ordered pairs. 

Mathematically, a function is a special kind of relation. 

Definition: A function is a relation between two variables such that the independent value has EXACTLY 
one dependent value. 

This usually means that each x- value has only one y— value assigned to it. But, not all functions involve 
x and y. 

Consider the relation that shows the heights of all students in a class. The domain is the set of people in 
the class and the range is the set of heights. Each person in the class cannot be more than one height at 
the same time. This relation is a function because for each person there is exactly one height that belongs 
to him or her. 



29 



www.ckl2.org 



Domain 

DJ 

Maya 

Ashleigh 

Victoria 

Vincent 

Ana Rojano 

Brandon 

Bryn 

Danna 

Alex 

Brain 

Ana Karen 



Range 




-* 62 


inches 


?* 72 


inches 


^ 70 


inches 


^65 


inches 


^J60 


inches 


-5 58 


inches 


^r 64 


inches 


^68 


inches 



Notice that in a function, a value in the range can belong to more than one element in the domain, so more 
than one person in the class can have the same height. The opposite is not possible, one person cannot 
have multiple heights. 

Example 4: Determine if the relation is a function. 

a) (1, 3), (-1, -2), (3, 5), (2, 5), (3, 4) 

b) (-3, 20), (-5, 25), (-1, 5), (7, 12), (9, 2) 
Solution: 

a) To determine whether this relation is a function, we must follow the definition of a function. Each 
x-coordinate can have ONLY one y-coordinate. However, since the x-coordinate of 3 has two y-coordinates, 
4 and 5, this relation is NOT a function. 

b) Applying the definition of a function, each x-coordinate has only one y-coordinate. Therefore, this 
relation is a function. 



Determining Whether a Graph Is a Function 



One way to determine whether a relation is a function is to construct a flow chart linking each dependent 
value to its matching independent value. Suppose, however, all you are given is the graph of the relation. 
How can you determine whether it is a function? 

You could organize the ordered pairs into a table or a flow chart, similar to the student and height situation. 
This could be a lengthy process, but it is one possible way. A second way is to use the Vertical Line 
Test. Applying this test gives a quick and effective visual to decide if the graph is a function. 

Theorem: Part A) A relation is a function if there are no vertical lines that intersect the graphed relation 
in more than one point. 

Part B) If a graphed relation does not intersect a vertical line in more than one point, then that relation 
is a function. 

Is this graphed relation a function? 



www.ckl2.org 



30 













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By drawing a vertical line (the red line) through the graph, we can see that the vertical line intersects the 
circle more than once. Therefore, this graph is NOT a function. 

Here is a second example: 



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i j 




t-t 


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No matter where a vertical line is drawn through the graph, there will be only one intersection. Therefore, 
this graph is a function. 

Example 4: Determine if the relation is a function. 











b- 














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3 


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Solution: Using the Vertical Line Test, we can conclude the relation is a function. 
For more information: 

Watch this YouTube video giving step-by-step instructions of the Vertical Line Test. CK-12 

Basic Algebra: Vertical Line Test (3:11) 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 



31 



www.ckl2.org 




Figure 1.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/715 

number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Functions as Graphs (9:34) 




Figure 1.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/716 

In 1 - 5, plot the coordinate points on the Cartesian plane. 

1. (4, -4) 

2. (2, 7) 

3. (-3, -5) 

4. (6, 3) 

5. (-4, 3) 

Using the coordinate plane below, give the coordinates for a - e. 



6. 



H — I — + — I — t — + — I- 



-8-7-6-5-4-3-2-1 .. 1 2 3 4 5 6 7 
-2 



b . 



-I — + — < » t — I — H*X 



In 7 - 9, graph the relation on a coordinate plane. According to the situation, determine whether to 
connect the ordered pairs with a smooth curve or leave as a scatter plot. 



www.ckl2.org 



32 



7. 



X 


-10 


-5 





5 


10 


Y 


-3 


-0.5 


2 


4.5 


7 



Table 1.4: 



Side of cube (in inches) 



Volume of cube (in inches 3 ) 




1 
2 
3 
4 




1 

8 

27 

64 



Table 1.5: 



Time (in hours) 



Distance (in miles) 




1 
2 



-50 

25 



5 
50 



In 10 - 12, graph the function. 

10. Brandon is a member of a movie club. He pays a $50 annual membership and $8 per movie. 

11. f{x) = (x-2f 

12. f(x) = 3.2* 

In 13 - 16, determine if the relation is a function. 

13. (1, 7), (2, 7), (3, 8), (4, 8), (5, 9) 

14. (1, 1), (1, -1), (4, 2), (4, -2), (9, 3), (9, -3) 
15. 



16. 



Age 


20 


25 




25 


30 


35 


Number of jobs by that age 


3 


4 




7 


4 


2 


x -4 


-3 




-2 




-1 





y 16 


9 




4 




1 






In 17 and 18, write a function rule for the graphed relation. 



33 



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19. The students at a local high school took the Youth Risk Behavior Survey. The graph below shows the 
percentage of high school students who reported that they were current smokers. A person qualifies 
as a current smoker if he/she has smoked one or more cigarettes in the past 30 days. What percentage 
of high school students were current smokers in the following years? 

(a) 1991 

(b) 1996 

(c) 2004 

(d) 2005 



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1996 2000 
Year 



20. The graph below shows the average lifespan of people based on the year in which they were born. This 
information comes from the National Vital Statistics Report from the Center for Disease Control. 
What is the average lifespan of a person born in the following years? 



(a) 1940 
www.ckl2.org 



34 



(b) 1955 

(c) 1980 

(d) 1995 



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1920 19 


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21. The graph below shows the median income of an individual based on his/her number of years of 
education. The top curve shows the median income for males and the bottom curve shows the 
median income for females (Source: US Census, 2003). What is the median income of a male who 
has the following years of education? 

(a) 10 years of education 

(b) 17 years of education 

What is the median income of a female who has the same years of education? 

(c) 10 years of education 

(d) 17 years of education 



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years of education 



In 22 - 23, determine whether the graphed relation is a function. 



22. 



mm 

_i_LeJ — 



35 



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23. 











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24. A theme park charges $12 entry to visitors. Find the money taken if 1296 people visit the park. 

25. A group of students are in a room. After 25 students leave, it is found that | of the original group 
are left in the room. How many students were in the room at the start? 

26. Evaluate the expression: 



x^+9 



3 and x = 4. 



27. The amount of rubber needed to make a playground ball is found by the formula A = 47rr 2 , where 
r = radius. Determine the amount of material needed to make a ball with a 7-inch radius. 



1.7 A Problem-Solving Plan 



Much of mathematics apply to real- world situations. To think critically and to problem solve are mathemat- 
ical abilities. Although these capabilities may be the most challenging, they are also the most rewarding. 

To be successful in applying mathematics in real-life situations, you must have a "toolbox" of strategies 
to assist you. The last few lessons of many chapters in this FlexBook are devoted to filling this toolbox so 
you to become a better problem solver and tackle mathematics in the real world. 



Step #1: Read and Understand the Given Problem 

Every problem you encounter gives you clues needed to solve it successfully. Here is a checklist you can 
use to help you understand the problem. 

V Read the problem carefully. Make sure you read all the sentences. Many mistakes have been made by 
failing to fully read the situation. 

V Underline or highlight key words. These include mathematical operations such as sum, difference, 
product, and mathematical verbs such as equal, more than, less than, is. Key words also include the nouns 
the situation is describing such as time, distance, people, etc. 

V Ask yourself if you have seen a problem like this before. Even though the nouns and verbs may be 
different, the general situation may be similar to something else you've seen. 

V What are you being asked to do? What is the question you are supposed to answer? 

V What facts are you given? These typically include numbers or other pieces of information. 

Once you have discovered what the problem is about, the next step is to declare what variables will 
represent the nouns in the problem. Remember to use letters that make sense! 



www.ckl2.org 



36 



Step #2: Make a Plan to Solve the Problem 

The next step in the problem-solving plan is to make a plan or develop a strategy. How can the 

information you know assist you in figuring out the unknown quantities? 

Here are some common strategies that you will learn. 




Drawing a diagram 

Making a table 

Looking for a pattern 

Using guess and check 

Working backwards 

Using a formula 

Reading and making graphs 

Writing equations 

Using linear models 

Using dimensional analysis 

Using the right type of function for the situation 

In most problems, you will use a combination of strategies. For example, drawing a diagram and looking 
for patterns are good strategies for most problems. Also, making a table and drawing a graph are often 
used together. The "writing an equation" strategy is the one you will work with the most frequently in 
your study of algebra. 

Step #3: Solve the Problem and Check the Results 

Once you develop a plan, you can use it to solve the problem. 

The last step in solving any problem should always be to check and interpret the answer. Here are some 
questions to help you to do that. 

• Does the answer make sense? 

• If you substitute the solution into the original problem, does it make the sentence true? 

• Can you use another method to arrive at the same answer? 

Step #4: Compare Alternative Approaches 

Sometimes a certain problem is best solved by using a specific method. Most of the time, however, it can be 
solved by using several different strategies. When you are familiar with all of the problem-solving strategies, 
it is up to you to choose the methods that you are most comfortable with and that make sense to you. In 
this book, we will often use more than one method to solve a problem. This way we can demonstrate the 
strengths and weaknesses of different strategies when applied to different types of problems. 

Regardless of the strategy you are using, you should always implement the problem-solving plan when you 
are solving word problems. Here is a summary of the problem-solving plan. 

37 www.ckl2.org 



Step 1: Understand the problem. 

Step 2: Devise a plan - Translate. Come up with a way to solve the problem. Set up an equation, draw 
a diagram, make a chart, or construct a table as a start to begin your problem-solving plan. 

Step 3: Carry out the plan - Solve. 

Step 4: Check and Interpret: Check to see if you have used all your information. Then look to see if the 
answer makes sense. 



Solve Real- World Problems Using a Plan 

Example 1: Jeff is 10 years old. His younger brother, Ben, is 4 years old. How old will Jeff be when he 
is twice as old as Ben? 

Solution: Begin by understanding the problem. Highlight the key words. 

Jeff is 10 years old. His younger brother, Ben, is 4 years old. How old will Jeff be when he is twice 
as old as Ben? 

The question we need to answer is. "What is Jeff's age when he is twice as old as Ben?" 

You could guess and check, use a formula, make a table, or look for a pattern. 

The key is "twice as old." This clue means two times, or double Ben's age. Begin by doubling possible 
ages. Let's look for a pattern. 

4x2 = 8. Jeff is already older than 8. 

5 x 2 = 10. This doesn't make sense because Jeff is already 10. 

6 x 2 = 12. In two years, Jeff will be 12 and Ben will be 6. Jeff will be twice as old. 

Jeff will be 12 years old. 

Example 2: Matthew is planning to harvest his corn crop this fall. The field has 660 rows of corn with 
300 ears per row. Matthew estimates his crew will have the crop harvested in 20 hours. How many ears of 
corn will his crew harvest per hour? 




Solution: Begin by highlighting the key information. 

Matthew is planning to harvest his corn crop this fall. The field has 660 rows of corn with 300 ears per 
row. Matthew estimates his crew will have the crop harvested in 20 hours. How many ears of corn 
will his crew harvest per hour? 

www.ckl2.org 38 



You could draw a picture (it may take a while), write an equation, look for a pattern, or make a table. 
Let's try to use reasoning. 

We need to figure out how many ears of corn are in the field. 660(300) = 198,000. This is how many ears 
are in the field. It will take 20 hours to harvest the entire field, so we need to divide 198,000 by 20 to get 
the number of ears picked per hour. 



198,000 
20 



9,900 



The crew can harvest 9,900 ears per hour. 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Word Problem-Solving Plan 1 (10:12) 




Figure 1.10: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/719 



1. What are the four steps to solving a problem? 

2. Name three strategies you can use to help make a plan. Which one(s) are you most familiar with 
already? 

3. Which types of strategies work well together? Why? 

4. Suppose Matthew's crew takes 36 hours to harvest the field. How many ears per hour will they 
harvest? 

5. Why is it difficult to solve Ben and Jeff's age problem by drawing a diagram? 

6. How do you check a solution to a problem? What is the purpose of checking the solution? 

7. There were 12 people on a jury, with four more women than men. How many women were there? 

8. A rope 14 feet long is cut into two pieces. One piece is 2.25 feet longer than the other. What are the 
lengths of the two pieces? 

9. A sweatshirt costs $35. Find the total cost if the sales tax is 7.75%. 

10. This year you got a 5% raise. If your new salary is $45,000, what was your salary before the raise? 

11. It costs $250 to carpet a room that is 14 ft X 18 ft. How much does it cost to carpet a room that is 
9 /Y x 10 ft? 

12. A department store has a 15% discount for employees. Suppose an employee has a coupon worth $10 
off any item and she wants to buy a $65 purse. What is the final cost of the purse if the employee 
discount is applied before the coupon is subtracted? 

13. To host a dance at a hotel, you must pay $250 plus $20 per guest. How much money would you have 
to pay for 25 guests? 



39 



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14. It costs $12 to get into the San Diego County Fair and $1.50 per ride. If Rena spent $24 in total, 
how many rides did she go on? 

15. An ice cream shop sells a small cone for $2.92, a medium cone for $3.50, and a large cone for $4.25. 
Last Saturday, the shop sold 22 small cones, 26 medium cones, and 15 large cones. How much money 
did the store earn? 

16. The sum of angles in a triangle is 180 degrees. If the second angle is twice the size of the first angle 
and the third angle is three times the size of the first angle, what are the measures of the angles in 
the triangle? 

Mixed Review 



17. Choose an appropriate variable for the following situation: It takes Lily 45 minutes to bathe and 
groom a dog. How many dogs can she groom in an 9-hour day? 

18. Translate the following into an algebraic inequality: Fourteen less than twice a number is greater 
than or equal to 16. 

19. Write the pattern of the table below in words and using an algebraic equation. 



x 

y 



-2 



-1 
-4 








1 
4 



20. Check that m = 4 is a solution to 3y - 11 > -3. 

21. What is the domain and range of the graph below? 



y 


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1.8 Problem- Solving Strategies: Make a Table; 
Look for a Pattern 

This lesson focuses on two of the strategies introduced in the previous chapter: making a table and looking 
for a pattern. These are the most common strategies you have used before algebra. Let's review the 
four-step problem-solving plan from Lesson 1.7. 

Step 1: Understand the problem. 

Step 2: Devise a plan - Translate. Come up with a way to solve the problem. Set up an equation, draw 
a diagram, make a chart, or construct a table as a start to begin your problem-solving plan. 

Step 3: Carry out the plan - Solve. 

Step 4: Check and Interpret: Check to see if you used all your information. Then look to see if the answer 
makes sense. 



www.ckl2.org 



40 



Using a Table to Solve a Problem 

When a problem has data that needs to be organized, a table is a highly effective problem-solving strategy. 
A table is also helpful when the problem asks you to record a large amount of information. Patterns and 
numerical relationships are easier to see when data are organized in a table. 

Example 1: Josie takes up jogging. In the first week she jogs for 10 minutes per day, in the second week 
she jogs for 12 minutes per day. Each week, she wants to increase her jogging time by 2 minutes per day. 
If she jogs six days per week each week, what will be her total jogging time in the sixth week? 

Solution: Organize the information in a table 

Table 1.6: 



Week 1 



Week 2 



Week 3 



Week 4 



10 minutes 
60 min/week 



12 minutes 
72 min/week 



14 minutes 
84 min/week 



16 minutes 
96 min/week 



We can see the pattern that the number of minutes is increasing by 12 each week. Continuing this pattern, 
Josie will run 120 minutes in the sixth week. 

Don't forget to check the solution! The pattern starts at 60 and adds 12 each week after the first week. 
The equation to represent this situation is t = 60 + 12(w - 1). By substituting 6 for the variable of w, the 
equation becomes t = 60 + 12(6 - 1) = 60 + 60 = 120 



Solve a Problem by Looking for a Pattern 

Some situations have a readily apparent pattern, which means that the pattern is easy to see. In this case, 
you may not need to organize the information into a table. Instead, you can use the pattern to arrive at 
your solution. 

Example 2: You arrange tennis balls in triangular shapes as shown. How many balls will there be in a 
triangle that has 8 layers? 




1 layer 2 layer 3 layer 

One layer: It is simple to see that a triangle with one layer has only one ball. 




Two layers: For a triangle with two layers we add the balls from the top layer to the balls of the bottom 
layer. It is useful to make a sketch of the different layers in the triangle. 




=2+1=3 



Top 
layer 



Bottom 
layer 



41 



www.ckl2.org 



Three layers: we add the balls from the top triangle to the balls from the bottom layer. 

* ©©©-**»- 





We can fill the first three rows of the table. 

12 3 4 

1 3 6 6 + 4 = 10 

To find the number of tennis balls in 8 layers, continue the pattern. 

5 6 7 8 

10 + 5 = 15 15 + 6 = 21 21 + 7 = 28 28 + 8 = 36 

There will be 36 tennis balls in the 8 layers. 

Check: Each layer of the triangle has one more ball than the previous one. In a triangle with 8 layers, 
each layer has the smae number of balls as its position. When we add these we get: 

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 36 balls 

The answer checks out. 

Comparing Alternative Approaches to Solving Problems 

In this section, we will compare the methods of "Making a Table" and "Looking for a Pattern" by using 
each method in turn to solve a problem. 

Example 3: Andrew cashes a $180 check and wants the money in $10 and $20 bills. The bank teller gives 
him 12 bills. How many of each kind of bill does he receive? 

Solution: Method 1: Making a Table 

Tens 2 

Twenties 9 8 

The combination that has a sum of 12 is six $10 bills and six $20 bills. 

Method 2: Using a Pattern 

The pattern is that for every pair of $10 bills, the number of $20 bills reduces by one. Begin with the most 
number of $20 bills. For every $20 bill lost, add two $10 bills. 

6($10) + 6($20) = $180 
Check: Six $10 bills and six $20 bills = 6($10) + 6($20) = $60 + $120 = $180. 

Using These Strategies to Solve Problems 

Example 4: Students are going to march in a homecoming parade. There will be one kindergartener, two 
first- graders, three second- graders, and so on through VI th grade. How many students will be walking in the 
homecoming parade? 

www.ckl2.org 42 



4 


6 


8 


10 


12 


14 


16 


18 


7 


6 


5 


4 


3 


2 


1 






Could you make a table? Absolutely. Could you look for a pattern? Absolutely. 
Solution 1: Make a table: 



K 

1 



3 
4 



4 

5 



5 
6 



6 

7 



9 



9 
10 



10 
11 



11 
12 



12 
13 



The solution is the sum of all the numbers, 91. There will be 91 students walking in the homecoming 
parade. 

Solution 2: Look for a pattern. 

The pattern is: The number of students is one more than their grade level. Therefore, the solution is the 
sum of numbers from 1 (kindergarten) through 13 (12 r/l grade). The solution is 91. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Word Problem-Solving Strategies (12:51) 




Figure 1.11: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/722 



1. Go back and find the solution to the problem in Example 1. 

2. Britt has $2.25 in nickels and dimes. If she has 40 coins in total how many of each coin does she 
have? 

3. A pattern of squares is placed together as shown. How many squares are in the 12 fft diagram? 



□ 



4. Oswald is trying to cut down on drinking coffee. His goal is to cut down to 6 cups per week. If he 
starts with 24 cups the first week, cuts down to 21 cups the second week, and drops to 18 cups the 
third week, how many weeks will it take him to reach his goal? 

5. Taylor checked out a book from the library and it is now 5 days late. The late fee is 10 cents per 
day. How much is the fine? 

6. How many hours will a car traveling at 75 miles per hour take to catch up to a car traveling at 55 
miles per hour if the slower car starts two hours before the faster car? 

7. Grace starts biking at 12 miles per hour. One hour later, Dan starts biking at 15 miles per hour, 
following the same route. How long would it take him to catch up with Grace? 



43 



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8. Lemuel wants to enclose a rectangular plot of land with a fence. He has 24 feet of fencing. What is 
the largest possible area that he could enclose with the fence? 

Mixed Review 

9. Determine if the relation is a function: {(2, 6), (-9, 0), (7, 7), (3, 5), (5, 3)} . 

10. Roy works construction during the summer and earns $78 per job. Create a table relating the number 
of jobs he could work, j, and the total amount of money he can earn, m. 

11. Graph the following order pairs: (4,4); (-5,6), (-1,-1), (-7,-9), (2,-5) 

12. Evaluate the following expression: -4(4z - x + 5); use x = -10, and z = -8. 

13. The area of a circle is given by the formula A = 7ir 2 . Determine the area of a circle with radius 6 
mm. 

14. Louie bought 9 packs of gum at $1.19 each. How much money did he spend? 

15. Write the following without the multiplication symbol: 16 x gC. 

1.9 Chapter 1 Review 

Define the following words: 

1. Domain 

2. Range 

3. Solution 

4. Evaluate 

5. Substitute 

6. Operation 

7. Variable 

8. Algebraic expression 

9. Equation 

10. Algebraic inequality 

11. Function 

12. Independent variable 

Evaluate the following expressions. 

13. 3y(7 - (z - y)); use y = -7 and z = 2 

14. m £~ p ; use m = 9, n = 7, and p = 2 

o 

15. \p\ - (|J ; use n = 2 and p = 3 

16. |v-21|, v = -70 

Choose an appropriate variable to describe the situation. 

17. The number of candies you can eat in a day 

18. The number of tomatoes a plant can grow 

19. The number of cats at a humane society 

20. The amount of snow on the ground 

21. The number of water skiers on a lake 

22. The number of geese migrating south 

www.ckl2.org 44 



23. The number of people at a trade show 

The surface area of a sphere is found by the formula A = Anr 2 . Determine the surface area for the following 
radii/diameters. 

24. radius = 10 inches 

25. radius = 2.4 cm 

26. diameter = 19 meters 

27. radius = 0.98 mm 

28. diameter = 5.5 inches 

Insert parentheses to make a true equation. 

29. 1 + 2-3 + 4= 15 

30. 5 • 3 - 2 + 6 = 35 

31. 3 + 1-7- 2 2 -9-7 = 24 

32. 4 + 6-2-5-3 = 40 

33. 3 2 + 2 -7-4 = 33 

Translate the following into an algebraic equation or inequality. 

34. Thirty-seven more than a number is 612. 

35. The product of u and -7 equals 343. 

36. The quotient of k and 18 

37. Eleven less than a number is 43. 

38. A number divided by -9 is -78. 

39. The difference between 8 and h is 25. 

40. The product of 8, -2, and r 

41. Four plus m is less than or equal to 19. 

42. Six is less than c. 

43. Forty-two less than y is greater than 57. 

Write the pattern shown in the table with words and with an algebraic equation. 
44. 



Movies watched 





1 


2 


3 


4 


5 


Total time 





1.5 


3 


4.5 


6 


7.5 



45. A case of donuts is sold by the half-dozen. Suppose 168 people purchase cases of donuts. How many 
individual donuts have been sold? 

46. Write an inequality to represent the situation: Peter's Lawn Mowing Service charges $10 per mowing 
job and $35 per landscaping job. Peter earns at least $8,600 each summer. 

Check that the given number is a solution to the given equation or inequality. 

47. f = 0.9, 54 < 7(9; + 5) 

48. / = 2; / + 2 + 5/=14 

49. p = -6; 4p - 5p < 5 

45 www.ckl2.org 



50. Logan has a cell phone service that charges $18 dollars per month and $0.05 per text message. 
Represent Logan's monthly cost as a function of the number of texts he sends per month. 

51. An online video club charges $14.99 per month. Represent the total cost of the video club as a 
function of the number of months that someone has been a member. 

52. What is the domain and range for the following graph? 

y 



m 



-10 -8-6-4-2 2 4 6 8 10 

53. Henry invested $5,100 in a vending machine service, 
machines does Henry need to install to break even? 

54. Is the following relation a function? 



Each machine pays him $128. How many 



§ 



Solve the following questions using the 4-step problem-solving plan. 



55. Together, the Raccoons and the Pelicans won 38 games. If the Raccoons won 13 games, how many 
games did the Pelicans win? 

56. Elmville has 250 fewer people than Maplewood. Elmville has 900 people. How many people live in 
Maplewood? 

57. The cell phone Bonus Plan gives you 4 times as many minutes as the Basic Plan. The Bonus Plan 
gives you a total of 1200 minutes. How many minutes does the Basic Plan give? 

58. Margarite exercised for 24 minutes each day for a week. How many total minutes did Margarite 
exercise? 

59. The downtown theater costs $1.50 less than the mall theater. Each ticket at the downtown theater 
costs $8. How much do tickets at the mall theater cost? 

60. Mega Tape has 75 more feet of tape than everyday tape. A roll of Mega Tape has 225 feet of tape. 
How many feet does everyday tape have? 

61. In bowling DeWayne got 3.5 times as many strikes as Junior. If DeWayne got 28 strikes, how many 
strikes did Junior get? 



www.ckl2.org 



46 



1.10 Chapter 1 Test 



1. Write the following as an algebraic equation and determine its value. On the stock market, Global 
First hit a price of $255 on Wednesday. This was $59 greater than the price on Tuesday. What was 
the price on Tuesday? 

2. The oak tree is 40 feet taller than the maple. Write an expression that represents the height of the 
oak. 

3. Graph the following ordered pairs: (1, 2), (2, 3), (3, 4), (4, 5) (5, 6), (6, 7). 

4. Determine the domain and range of the following function: 




2 3 4 5 
longest side 

5. Is the following relation a function? Explain your answer. {(3,2), (3,4), (5,6), (7,8)} 

6. Evaluate the expression if a = 2, b = 3, c = 4; (5bc) - a. 

7. Simplify: 3[36 -=- (3 + 6)]. 

8. Translate into an algebraic equation and find the value of the variable. One-eighth of a pizza costs 
$1.09. How much was the entire pizza? 

9. Use the 4-step problem-solving method to determine the solution: The freshman class has 11 more 
girls than boys. There are 561 freshmen. How many are girls? 

10. Underline the math verb in this sentence: The quotient of 8 and y is 48. 

11. Jesse packs 16 boxes per hour. Complete the table to represent this situation. 



Hours 
Boxes 







10 



12 



14 



12. A group of students are in a room. After 18 leave, it is found that I of the original number of 
students remain. How many students were in the room in the beginning? 

13. What are the domain and range of the following relation: {(2, 3), (4, 5), (6, 7), (-2, -3), (-3, -4)}? 

14. Write a function rule for the table: 



Time in hours, x 





1 


2 


3 


4 


Distance in miles, y 





60 


120 


180 


240 



15. Determine if the given number is a solution to the inequality: — - > -8; y = 6 



Image Sources 



(1) http : //www . publicdomainpictures . net /view- image . php?image=1559&#38 ; picture= 
christmas-baubles. 



47 



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Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/flexr/chapter/9611. 



www.ckl2.org 48 



Chapter 2 

Properties of Real Numbers 



Real numbers are all around us. The majority of numbers calculated are considered real numbers. This 
chapter defines a real number and explains important properties and rules that apply to real numbers. 

2.1 Integers and Rational Numbers 

Integers and rational numbers are important in daily life. The price per square yard of carpet is a rational 
number. The number of frogs in a pond is expressed using an integer. The organization of real numbers 
can be drawn as a hierarchy. Look at the hierarchy below. 



> 



Rational Numbers 



Real Numbers 




Irrational Numbers 



Whole 
Numbers 



Counting 
Numbers 



The most generic number is the real number; it can be a combination of negative, positive, decimal, 
fractional, or non-repeating decimal values. Real numbers have two major categories: rational numbers 
and irrational numbers. Irrational numbers are non-repeating, non-terminating decimals such as n or 
v2. The discussion in this lesson revolves around rational numbers. 

Definition: A rational number is a number that can be written in the form |, where a and b are integers 



49 



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and b ± 0. 



A Review of Fractions 

You can think of a rational number as a fraction of a cake. If you cut the cake into b slices, your share is 
a of those slices. For example, when we see the rational number |, we imagine cutting the cake into two 
parts. Our share is one of those parts. Visually, the rational number \ looks like this. 




There are three main types of fractions: 

• Proper fractions are rational numbers where the numerator is less than the denominator. A proper 
fraction represents a number less than one. With a proper fraction you always end up with less than 
a whole cake! 

• Improper fractions are rational numbers where the numerator is greater than the denominator. 
Improper fractions can be rewritten as a mixed number - an integer plus a proper fraction. An 
improper fraction represents a number greater than one. 

• Equivalent fractions are two fractions that give the same numerical value when evaluated. For 
example, look at a visual representation of the rational number -g. 




The visual of \ is equivalent to the visual of |. We can write out the prime factors of both the numerator 
and the denominator and cancel matching factors that appear in both the numerator and denominator. 

(I) = (t~M We then re-multiply the remaining factors. \V\ = \hj 



Therefore, \ 



|. This process is called reducing the fraction, or writing the fraction in lowest terms. 



Reducing a fraction does not change the value of the fraction; it simplifies the way we write it. When we 
have canceled all common factors, we have a fraction in its simplest form. 

Example 1: Classify and simplify the following rational numbers. 

a )(i) 

b)(!) 

c)(i) 
Solution: 



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50 



a) Because both 3 and 7 are prime numbers, I is a proper fraction written in its simplest form. 

b) The numerator is larger than the denominator; therefore, this is an improper fraction. 

9 _ 3^3 
3 ~ ~3~ 



I- 



c) This is a proper fraction; |2 = §^§|f = - 



Ordering Rational Numbers 

To order rational numbers is to arrange them according to a set of directions, such as ascending (lowest to 
highest) or descending (highest to lowest). Ordering rational numbers is useful when determining which 
unit cost is the cheapest. 

Example 2: Cans of tomato sauce come in three sizes: 8 ounces, 16 ounces, and 32 ounces. The costs 
for each size are $0.59, $0.99, and $1.29, respectively. Find the unit cost and order the rational numbers 
in ascending order. 

Solution: Use proportions to find the cost per ounce. M = $™Z375. m* _ $M61875. M _ $Q.Q4Q3125 



16 



0.061875 . $1.29 
ounce ' 32 



Arranging the rational numbers in ascending order: 0.0403125, 0.061875, 0.07375 

Example 3: Which is greater | or |? 

Solution: Begin by creating a common denominator for these two fractions. Which number is evenly 
divisible by 7 and 9? 7 X 9 = 63, therefore the common denominator is 63. 

3x9_27 4x7_28 

~" 63 ~ ~~ 



7x9 



9x7 63 



Because 28 > 27, | > f 



For more information regarding how to order fractions, watch this YouTube video. 
Khan Academy: Ordering Fractions 




Figure 2.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/724 



Graph and Compare Integers 

More specific than the rational numbers are the integers. Integers are whole numbers and their negatives. 
When comparing integers, you will use the math verbs such as less than, greater than, approximately 
equal to, and equal to. To graph an integer on a number line, place a dot above the number you want to 
represent. 

Example 4: Compare the numbers 2 and -5. 



51 



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Solution: First, we will plot the two numbers on a number line. 
The number -5 The number 2 

\ \ 

♦ i i i i i i ♦ i i i i ■ 



-6-5-4-3-2-101234 56 

We can compare integers by noting which is the greatest and which is the least. The greatest number 
is farthest to the right, and the least is farthest to the left. 

In the diagram above, we can see that 2 is farther to the right on the number line than -5, so we say that 
2 is greater than -5. We use the symbol > to mean "greater than." 

Therefore, 2 > -5. 

Numbers and Their Opposites 

Every number has an opposite, which represents the same distance from zero but in the other direction. 
These numbers are opposites 



-6-5-4-3-2-10123456 

A special situation arises when adding a number to its opposite. The sum is zero. This is summarized in 
the following property. 

The Additive Inverse Property: For any real number a, a + (-a) = 0. 

Absolute Value 

Absolute value represents the distance from zero when graphed on a number line. For example, the 
number 7 is 7 units away from zero. The number -7 is also 7 units away from zero. The absolute value of 
a number is the distance it is from zero, so the absolute value of 7 and the absolute value of -7 are both 7. 

We write the absolute value of -7 like this | - 7| 

We read the expression \x\ like this: "the absolute value of jc." 

• Treat absolute value expressions like parentheses. If there is an operation inside the absolute value 
symbols, evaluate that operation first. 

• The absolute value of a number or an expression is always positive or zero. It cannot be negative. 
With absolute value, we are only interested in how far a number is from zero, not the direction. 

Example 5: Evaluate the following absolute value expressions. 

a) |5 + 4| 

b) 3 - |4 - 9| 

c) I -5- 11| 

d) -|7-22| 
Solution: 

www.ckl2.org 52 



|5 + 4| = |9| 
= 9 



b) 



3 - |4 - 9| = 3 - | - 5| 
= 3-5 
= -2 



5- 11| = |-16| 
= 16 



d) 



-|7 -22| = -| -15| 
= -(15) 
= -15 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Integers and Rational Numbers (13:00) 




Figure 2.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/725 



1. Define absolute value. 

2. What are the three types of fractions? 

3. Give an example of a real number that is not an integer. 

4. What standards separate a rational number from an irrational number? 

5. The tick-marks on the number line represent evenly spaced integers. Find the values oia,b,c,d, and 



e. 



I I I I I I I I I > 

a b c d e 21 



In 6 - 8, determine what fraction of the whole each shaded region represents. 

53 



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In 9 - 12, place the following sets of rational numbers in order from least to greatest. 



9. 
10. 
11. 

12. 



ill 

ii¥i3 
WWk 

60' 80' 100 



11' 13' 19 

In 13 - 18, find the simplest form of the following rational numbers. 



13. 
14. 
15. 
16. 
17. 
18. 



22 
4 9 4 



J?5 

11 



In 19 - 24, find the opposite of each of the following. 

19. 1.001 

20. -9.345 

21. (16-45) 

22. (5- 11) 

23. (x + y) 

24. (x-y) 



In 25 - 34, simplify. 
www.ckl2.org 



54 



25. 


| - 98.4| 


26. 


|123.567| 


27. 


-|16 - 98| 


28. 


11-1-41 


29. 


|4-9| -|-5| 


30. 


1-5-111 


31. 


7-|22-15-19| 


32. 


-|-7| 


33. 


| - 2 - 88| - |88 + 2| 


34. 


|-5-99| + -|16-7| 



In 35 - 38, compare the two real numbers. 

35. 8 and 7.99999 

36. -4.25 and =f- 

37. 65 and -1 

38. 10 units left of zero and 9 units right of zero 

39. A frog is sitting perfectly on top of number 7 on a number line. The frog jumps randomly to the left 
or right, but always jumps a distance of exactly 2. Describe the set of numbers that the frog may land 
on, and list all the possibilities for the frog's position after exactly 5 jumps. 

Initi f' Possible jump 
position 






01 234 5678 9 10 11 

40. Will a real number always have an additive identity? Explain your reasoning. 

Mixed Review 

41. Evaluate the following expression: |d + 7a 2 ; use a = (-1), d = 24. 

42. The length of a rectangle is one more inch than its width. If the perimeter is 22 inches, what are the 
dimensions of the rectangle? 

43. Determine if x = -2 is a solution to 4x + 7 < 15. 

a a C- rr (7+3)+2x3 2 -5 

44. Simplify: ( ^ 8 _ 8) • 

2.2 Addition of Rational Numbers 

A football team gains 11 yards on one play then loses 5 yards on another play and loses 2 yards on the 
third play. What is the total yardage loss or gain? 

A loss can be expressed as a negative integer. A gain can be expressed as a positive integer. To find the 
net gain or loss, the individual values must be added together. Therefore, the sum is 11 + (-5) + (-2) = 4. 
The team has a net gain of 4 yards. 

Addition can also be shown using a number line. If you need to add 2 + 3, start by making a point at the 
value of 2 and move three integers to the right. The ending value represents the sum of the values. 

55 www.ckl2.org 



El 




-6 -5 -4 -3 -2 -1 1 [U 3 4 5 6 

Example 1: Find the sum of -2 + 3 using a number line. 

Solution: Begin by making a point at -2 and moving three units to the right. The final value is 1, so 
-2 + 3 = 1. 

m 



i i i 4TT) i i i i i 



-6-5-4-3^-101234 56 

When the value that is being added is positive, we jump to the right. If the value is negative, we jump to 
the left (in a negative direction). 

Example 2: Find the sum of 2 - 3 using a number line. 

Solution: Begin by making a point at 2. The expression represents subtraction, so we will count three 
jumps to the left. 

ED 




-6 -5 -4 -3 -2 -1 1 [I] 3 4 5 6 

The solution is: 2 - 3 = -1 

Algebraic Properties of Addition 

In Lesson 2.1, you learned the Additive Inverse Property. This property states that the sum of a number and 
its opposite is zero. Algebra has many other properties that help you manipulate and organize information. 

The Commutative Property of Addition: For all real numbers a, and Z?, a + b = b + a. 

To commute means to change locations, so the Commutative Property of Addition allows you to rearrange 
the objects in an addition problem. 

The Associative Property of Addition: For all real numbers a, b, and c, (a + b) + c = a + (b + c). 

To associate means to group together, so the Associative Property of Addition allows you to regroup the 
objects in an addition problem. 

The Identity Property of Addition: For any real number a, a-\- = a. 

This property allows you to use the fact that the sum of any number and zero is the original value. 

Example 3: Simplify the following using the properties of addition: 

a) 9 + (1 + 22) 

b) 4,211 + 

Solution: 

a) It is easier to regroup 9 + 1, so by applying the Associative Property of Addition, (9 + 1) + 22 = 10 + 22 = 
32. 

www.ckl2.org 56 



b) The Additive Identity Property states the sum of a number and zero is itself; therefore, 4, 211+0 = 4, 211. 

Nadia and Peter are building sand castles on the beach. Nadia built a castle two feet tall, stopped for 
ice-cream, and then added one more foot to her castle. Peter built a castle one foot tall before stopping 
for a sandwich. After his sandwich, he built up his castle by two more feet. Whose castle is the taller? 




Nadia's castle is (2 + 1) feet tall. Peter's castle is (1 + 2) feet tall. According to the Commutative 
Property of Addition, the two castles are the same height. 

Adding Rational Numbers 

To add rational numbers, we must first remember how to rewrite mixed numbers as improper fractions. 
Begin by multiplying the denominator of the mixed number to the whole value. Add the numerator to this 
product. This value is the numerator of the improper fraction. The denominator is the original. 

Example 4: Write 11 ^ as an improper fraction: 

Solution: 3x11 = 33 + 2 = 35. This is the numerator of the improper fraction. 

3 3 

Now that we know how to rewrite a mixed number as an improper fraction, we can begin to add rational 
numbers. There is one thing to remember when finding the sum or difference of rational numbers: The 
denominators must be equivalent. 

The Addition Property of Fractions: For all real numbers a, b, and c, - + - = q - £ ^-. 

Watch this video for further explanation on adding fractions with unlike denominators. This video shows 
how to add fractions using a visual model. 

http : //www . teachertube . com/viewVideo . php?video_id=103926&#38 ; t itle=Adding_Fract ions_with_ 
Unlike Denominators 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 



57 



www.ckl2.org 



number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Addition of Rational Numbers (7:40) 




Figure 2.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/727 

In exercises 1 and 2, write the sum represented by the moves on the number line. 



1. 



2. 




Find the sum. Write the answer in its simplest form. 



3. 


3,2 

7 ~r 7 


4. 
5. 


J, 1 

16 "•" 12 


6. 

7. 


3.9 

25 + 10 


8. 
9. 


i + i 


10. 


5,2 
19 " r 27 


11. 


-2.6 + 11.19 


12. 


-8 + 13 


13. 


-7.1 + (-5.63) 


14. 


9.99 + (-0.01) 


15. 


4 I + ^ 


16. 


-31 + (-2f) 



In 17 - 20, which property of addition does each situation involve? 

17. Whichever order your groceries are scanned at the store, the total will be the same. 

18. Suppose you go buy a DVD for $8.00, another for $29.99, and a third for $14.99. You can add 
(8 + 29.99) + 14.99 or you can add 8 + (29.99 + 14.99) to obtain the total. 



www.ckl2.org 



58 



19. Shari's age minus the negative of Jerry's age equals the sum of the two ages. 

20. Kerri has 16 apples and has added zero additional apples. Her current total is 16 apples. 

21. Nadia, Peter, and Ian are pooling their money to buy a gallon of ice cream. Nadia is the oldest and 
gets the greatest allowance. She contributes half of the cost. Ian is next oldest and contributes one 
third of the cost. Peter, the youngest, gets the smallest allowance and contributes one fourth of the 
cost. They figure that this will be enough money. When they get to the check-out, they realize that 
they forgot about sales tax and worry there will not be enough money. Amazingly, they have exactly 
the right amount of money. What fraction of the cost of the ice cream was added as tax? 

22. A blue whale dives 160 feet below the surface then rises 8 feet. Write the addition problem and find 
the sum. 

23. The temperature in Chicago, Illinois one morning was -8°F. Over the next six hours the temperature 
rose 25 degrees Fahrenheit. What was the new temperature? 

In 24 - 30, evaluate each expression for v = 5.8. 

24. 9.1 + v 

25. v+(-v) 

26. -v + 4.12 

27. -23.14 + -v 

28. 7.86 + (-v) 

29. -v + 3.5 

30. -v + v 

Mixed Review 

31. Find the opposite of -72. 

32. Evaluate |16 - 29 + 78 - 114|. 

33. What is the domain and range of the following: {(2, -1), (3, 0), (4, 6), (1, -3)}? 

34. Write a rule for the table: 

Table 2.1: 

Volume (in cubic inches) Mass (in grams) 

1 20.1 

2 40.2 

3 60.3 

4 80.4 



2.3 Subtraction of Rational Numbers 

In the previous two lessons, you have learned how to find the opposite of a rational number and to add 
rational numbers. You can use these two concepts to subtract rational numbers. Suppose you want to find 
the difference of 9 and 12. Symbolically, it would be 9 - 12. Begin by placing a dot at nine and move to 
the left 12 units. 

59 www.ckl2.org 



-10-9-8-7-6-5-4-3-2-1 1 2 3 4 5 6 7 8 9 10 

9 -12 = -3 

Rule: To subtract a number, add its opposite. 

3-5 = 3 + (-5) = -2 9 - 16 = 9 + (-16) = -7 

A special case of this rule can be written when trying to subtract a negative number. 

The Opposite-Opposite Property: For any real numbers a and b, a - (-b) = a + b. 

Example 1: Simplify -6 - (-13). 

Solution: Using the Opposite-Opposite Property, the double negative is rewritten as a positive. 

-6 -(-13) = -6 + 13 = 7 

Example 2: Simplify | - ( - xg)- 

Solution: Begin by using the Opposite-Opposite Property. 

5 J_ 

6 + 18 

Next, create a common denominator: ||| + jg = y§ + jz. 
Add the fractions: y|. 



Reduce: 



2x2x2x2 _ 8 
3x3x2 9* 



Evaluating Change Using a Variable Expression 

You have learned how to graph a function by using an algebraic expression to generate a table of values. 
Using the table of values you can find the change in the dependent values between any two independent 
values. 

In Lesson 1.5, you wrote an expression to represent the pattern of the total cost to the number of CDs 
purchased. The table is repeated below: 

Number of CDs 2 4 6 8 10 

Cost ($) 24 48 72 96 120 

To determine the change, you must find the difference between the dependent values and divide it by 
the difference in the independent values. 

Example 2: What is the cost of a CD? 

Solution: We begin by finding the difference between the cost of two values. For example, the change in 
cost between 4 CDs and 8 CDs. 

96 - 48 = 48 
Next, we find the difference between the number of CDs. 



48 
Finally, we divide. — = 12 



4 = 4 

18 
4~ 



www.ckl2.org 60 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Subtraction of Rational Numbers (10:22) 




Figure 2.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/728 

In 1 - 20, subtract the following rational numbers. Be sure that your answer is in the simplest form. 



1. 
2. 
3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 
24. 

25. 

26. 



9-14 

2-7 
21-8 



-14) 
(-50) 



-11 

JL _ JL 

12 18 

5.4-1.01 

2 _ 1 

I_? 

4 3 

15 _ 9 

11 7 

!L _ _L 

13 11 

JL _ JL 

27 39 
JL _ A 
11 22 

-3.1-21.49 

13 _ JL 

70 30 

-68 - (-22) 
l _ l 

3 2 

Determine the change in y between (1, 9) and (5, -14). 

Consider the equation y = 3x + 2. Determine the change in y between x = 3 and x = 7. 

Consider the equation y = |jc + \. Determine the change in y between x = 1 and jc = 2. 

True or false? If the statement is false, explain your reasoning. The difference of two numbers is less 

than each number. 

True or false? If the statement is false, explain your reasoning. A number minus its opposite is twice 

the number. 

KMN stock began the day with a price of $4.83 per share. At the closing bell, the price dropped 

$0.97 per share. What was the closing price of KMN stock? 



61 



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In 27 - 32, evaluate the expression. Assume a = 2, b = -3, and c = -1.5. 

27. (a - b) + c 

28. \b + c\-a 

29. a - (/? + c) 

30. |6| + |c| + fl 

31. 7b + 4a 

32. {c-a)-b 

Mixed Review 

33. Graph the following ordered pairs: {(0,0), (4,4), (7, 1), (3,8)}. Is the relation a function? 

34. Evaluate the expression when m = (-§) - 2 \ m - . 

35. Translate the following into an algebraic equation: Ricky has twelve more dollars than Stacy. Stacy 
has 5 less dollars than Aaron. The total of the friends 7 money is $62. 

36. Simplify \ + \- 

37. Simplify f - §. 

2.4 Multiplication of Rational Numbers 

When you began learning how to multiply whole numbers, you replaced repeated addition with the mul- 
tiplication sign (x). For example, 

6 + 6 + 6 + 6 + 6 = 5x6 = 30 

Multiplying rational numbers is performed the same way. We will start with the Multiplication Property 
of-1. 

The Multiplication Property of —1: For any real numbers a, (— 1) X a = -a. 

This can be summarized by saying, "A number times a negative is the opposite of the number." 

Example 1: Evaluate -1 • 9,876. 

Solution: Using the Multiplication Property of -1: -1 • 9,876 = -9,876. 

This property can also be used when the values are negative, as shown in Example 2. 

Example 2: Evaluate -1 • -322. 

Solution: Using the Multiplication Property of -1: -1 • -322 = 322. 

A basic algebraic property is the Multiplicative Identity. Similar to the Additive Identity, this property 
states that any value multiplied by 1 will result in the original value. 

The Multiplicative Identity Property: For any real numbers a, (1) X a — a. 

A third property of multiplication is the Multiplication Property of Zero. This property states that any 
value multiplied by zero will result in zero. 

The Zero Property of Multiplication: For any real numbers a, (0) Xa = 0. 

Multiplying Rational Numbers 

You've decided to make cookies for a party. The recipe you've chosen makes 6 dozen cookies, but you only 
need 2 dozen. How do you reduce the recipe? 

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In this case, you should not use subtraction to find the new values. Subtraction means to make less by 
taking away. You haven't made any cookies; therefore, you cannot take any away. Instead, you need to 
make | or ^ of the original recipe. This process involves multiplying fractions. 

For any real numbers a,b,c, and d, where b £ and d ± 0, 



a c 
V d 



ac 
bd 



Example 3: The original cookie recipe calls for 8 cups flour. How much is needed for the reduced recipe? 

Solution: Begin by writing the multiplication situation. 8 • |. You need to rewrite this product in the 
form of the property above. In order to perform this multiplication, you need to rewrite 8 as the fraction 



1 



8 1 
- x - 
1 3 



1 



1-3 



You will need 2 - cups flour. 



Multiplication of fractions can also be shown visually. For example, to multiply o 
represent the first fraction and a second model to represent the second fraction. 



|, draw one model to 



2_ 

5 



By placing one model (divided in thirds horizontally) on top of the other (divided in fifths vertically), you 
divide one whole rectangle into bd smaller parts. Shade ac smaller regions. 



The product of the two fractions is the 



shaded regions 
total regions ' 

1 2 
3 ' 5 



2 

15 



63 



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3 4 



Example 4: Simplify ^ • | 



3_ 

7 



4 

5 



3_ 4_ 
7 "5 



Solution: By drawing visual representations, you can see that 

3 4 _ 12 
7 ' 5 " 35 

Multiplication Properties 

Properties that hold true for addition such as the Associative Property and Commutative Property also 
hold true for multiplication. They are summarized below. 

The Associative Property of Multiplication: For any real numbers a, b, and c, 

(a- b) - c = a- (b • c) 

The Commutative Property of Multiplication: For any real numbers a and b, 

a(b) = b(a) 

The Same Sign Multiplication Rule: The product of two positive or two negative numbers is positive. 

The Different Sign Multiplication Rule: The product of a positive number and a negative number is 
a negative number. 

Solving Real- World Problems Using Multiplication 




Example 5: Anne has a bar of chocolate and she offers Bill a piece. Bill quickly breaks off \ of the bar 
and eats it. Another friend, Cindy, takes \ of what was left. Anne splits the remaining candy bar into two 
equal pieces, which she shares with a third friend, Dora. How much of the candy bar does each person get? 

Solution: Think of the bar as one whole. 



1- 



3 
4' 



This is the amount remaining after Bill takes his piece. 



k x I = I- This is the fraction Cindy receives. 



\. This is the amount remaining after Cindy takes her piece. 



Anne divides the remaining bar into two equal pieces. Every person receives | of the bar. 

Example 6: Doris's truck gets 10| miles per gallon. Her tank is empty so she puts in 5^ gallons of gas. 



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64 



How far can she travel? 

Solution: Begin by writing each mixed number as an improper fraction. 



2 32 
10- = — 

3 3 



1 11 
5 2 = T 



Now multiply the two values together. 



«. 11 = ^ = 581 = 58? 
3 2 6 6 3 



Doris can travel 58 g miles on 5.5 gallons of gas. 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Multiplication of Rational Numbers (8:56) 




Figure 2.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/729 



Multiply the following rational numbers. 



1. 





2 4 


2. 


-7.85 • -2.3 


3. 

4. 


2 5 

11 2 
3*7*5 


5. 


4.5 • -3 


6. 

7. 
8. 


12 3 4 

2*3*4*5 
5 v 9 

12 A 10 


9. 


2 v 1 

3 X 4 


10. 


-11.1(4.1) 


11. 


3 v 1 

4 3 


12. 


15 v 9 
11 X 7 

I • -3.5 


13. 


14. 
15. 

16. 


ivl 

V 3 * V 

27 A 14 

(If 


17. 


1 22 7 
11 * 21 A 10 



65 



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18. 5.75-0 



Multiply the following by negative one. 



19. 79.5 

20. 7i 

21. (x+1) 

22. |jc| 

23. 25 

24. -105 

25. x 2 

26. (3 + jc) 

27. (3-jc) 



In 28 - 30, state the property that applies to each of the following situations. 



28. A gardener is planting vegetables for the coming growing season. He wishes to plant potatoes and 
has a choice of a single 8 by 7 meter plot, or two smaller plots of 3 by 7 meters and 5 by 7 meters. 
Which option gives him the largest area for his potatoes? 

29. Andrew is counting his money. He puts all his money into $10 piles. He has one pile. How much 
money does Andrew have? 

30. Nadia and Peter are raising money by washing cars. Nadia is charging $3 per car, and she washes 
five cars in the first morning. Peter charges $5 per car (including a wax). In the first morning, he 
washes and waxes three cars. Who has raised the most money? 



Mixed Review 



31. Compare these rational numbers: ^| and |. 

32. Define rational numbers. 



33. Give an example of a proper fraction. How is this different from an improper fraction? 

34. Which property is being applied? 16 - (-14) = 16 + 14 = 30 

2 

9* 



35. Simplify 11 § + 2 



Quick Quiz 

1. Order from least to greatest: (|, ||, |^, ^j. 

2. Simplify § x f . 

3. Simplify |-5 + 11| -|9- 37|. 

4. Add f + f . 

www.ckl2.org 66 



2.5 The Distributive Property 




At the end of the school year, an elementary school teacher makes a little gift bag for each of his students. 
Each bag contains one class photograph, two party favors, and five pieces of candy The teacher will 
distribute the bags among his 28 students. How many of each item does the teacher need? 

You could begin this problem by deciding your variables. 

Let p = photograph, f = favors, and c = candy. 

Next you can write an expression to represent the situation: p + 2/ + 5c. 

There are 28 students in class, so the teacher needs to repeat the bag 28 times. An easier way to write 
this is 28- (p + 2f + 5c). 

We can omit the multiplication symbol and write 28 (p + 2/ + 5c). 

Therefore, the teacher needs 28/? + 28(2/) + 28(5c) or 28p + 56/ + 140c. 

The teacher needs 28 photographs, 56 favors, and 140 pieces of candy to complete the end-of-year gift bags. 

When you multiply an algebraic expression by another expression, you apply the Distributive Property. 

The Distributive Property: For any real expressions M, N, and K: 

M(N + K) = MN + MK 
M(N -K) = MN-MK 

Example 1: Determine the value o/ll(2 + 6) using both Order of Operations and the Distributive Property. 

Solution: Using the Order of Operations: 11(2 + 6) = 11(8) = 88. 

Using the Distributive Property: 11(2 + 6) = 11(2) + 11(6) = 22 + 66 = 88. 

Regardless of the method, the answer is the same. 

Example 2: Simplify 7(3x - 5). 

Solution 1: Think of this expression as seven groups of (3jc - 5). You could write this expression seven 
times and add all the like terms. (3x-5) + (3x-5) + (3x-5) + (3x-5) + (3x-5) + (3x-5) + (3x-5) = 21x-35 

Solution 2: Apply the Distributive Property. 7(3x - 5) = 7(3x) + 7(-5) = 21jc - 35 

Example 3: Simplify f (3y 2 - 11). 

Solution: Apply the Distributive Property. 

67 www.ckl2.org 



|(3j 2 + -11) = |(3y 2 ) + |(-11) 
6y 2 22 



Identifying Expressions Involving the Distributive Property 

The Distributive Property often appears in expressions, and many times it does not involve parentheses as 
grouping symbols. In Lesson 1.2, we saw how the fraction bar acts as a grouping symbol. The following 
example involves using the Distributive Property with fractions. 

Example 4: Simplify ^^. 

Solution: Think of the denominator as: ^^ = |(2jc + 4). 

Now apply the Distributive Property: |(2x) + ~(4) = ^f + |. 

Simplify: f + 1 



Solve Real- World Problems Using the Distributive Property 

The Distributive Property is one of the most common mathematical properties seen in everyday life. It 
crops up in business and in geometry. Anytime we have two or more groups of objects, the Distributive 
Property can help us solve for an unknown. 

Example 5: An octagonal gazebo is to be built as shown below. Building code requires five-foot-long steel 
supports to be added along the base and four-foot-long steel supports to be added to the roof-line of the 
gazebo. What length of steel will be required to complete the project? 

Solution: Each side will require two lengths, one of five and one of four feet respectively. There are eight 
sides, so here is our equation. 




Steel required = 8(4 + 5) feet. 

We can use the Distributive Property to find the total amount of steel. 

Steel required = 8 x 4 + 8 x 5 = 32 + 40 feet. 

A total of 72 feet of steel is needed for this project. 

www.ckl2.org 68 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Distributive Property (5:39) 




Figure 2.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/732 

Use the Distributive Property to simplify the following expressions. 

1. (x + 4)-2(x + 5) 

2. ^(42 + 6) 

3. (4 + 5) -(5 + 2) 

4. (x + 2 + 7) 

5. 0.25(6^ + 32) 

6. y(x + 7) 

7. -4.2(A-11) 

8. 13x(3v + z) 

9. \{x-y)-A 

10. 0.6(0.2x + 0.7) 

11. (2-;)(-6) 

12. (r + 3)(-5) 

13. 6 + (x-5) + 7 

14. 6-(x-5) + 7 

15. 4(m + 7) - 6(4 - m) 

16. -5(y-ll) + 2y 

Use the Distributive Property to simplify the following fractions. 

17 8x+12 
11 ■ 4 
■jo 9x+12 

20. 2Jf2 

91 fc-2 

Zl. 3 

22. 7 -^ 
In 23-25, write an expression for each phrase. 



23. I times the quantity of n plus 16 



69 



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24. Twice the quantity of m minus 3 

25. -Ax times the quantity of x plus 2 

26. A bookshelf has five shelves, and each shelf contains seven poetry books and eleven novels. How 
many of each type of book does the bookcase contain? 

27. Use the Distributive Property to show how to simplify 6(19.99) in your head. 

28. A student rewrote 4(9x + 10) as 36x + 10. Explain the student's error. 

29. Use the Distributive Property to simplify 9(5998) in your head. 

30. Amar is making giant holiday cookies for his friends at school. He makes each cookie with 6 oz 
of cookie dough and decorates each one with macadamia nuts. If Amar has 5 lbs of cookie dough 
(1 lb = 16 oz) and 60 macadamia nuts, calculate the following. 

(a) How many (full) cookies can he make? 

(b) How many macadamia nuts can he put on each cookie, if each is supposed to be identical? 




Mixed Review 

31. Translate into an inequality: Jacob wants to go to Chicago for his class trip. He needs at least $244 
for the bus, hotel stay, and spending money. He already has $104- How much more does he need to 
pay for his trip? 

32. Underline the math verb(s) in this sentence: The product of 6 and a number is 4 less than 16. 

33. Draw a picture to represent 3|. 

34. Determine the change in y of the equation y = \x- A between x = 3 and x = 9. 

2.6 Division of Rational Numbers 

So far in this chapter, you have added, subtracted, and multiplied rational numbers. It now makes sense 
to learn how to divide rational numbers. We will begin with a definition of inverse operations. 

Inverse operations "undo" each other. 

For example, addition and subtraction are inverse operations because addition cancels subtraction and vice 
versa. The additive identity results in a sum of zero. In the same sense, multiplication and division are 
inverse operations. This leads into the next property: The Inverse Property of Multiplication. 

The Inverse Property of Multiplication: For every nonzero number a, there is a multiplicative inverse 
- such that a(-) = 1. 

The values of a and ^ are called reciprocals. In general, two nonzero numbers whose product is 1 are 
reciprocals. 

Reciprocal: The reciprocal of a nonzero rational number | is ~. 

Note: The number zero does not have a reciprocal. 

www.ckl2.org 70 



Using Reciprocals to Divide Rational Numbers 

When dividing rational numbers, use the following rule: 

"When dividing rational numbers, multiply by the 'right' reciprocal." 

In this case, the "right" reciprocal means to take the reciprocal of the fraction on the right-hand side of 
the division operator. 

Example 1: Simplify | 4- I. 

Solution: Begin by multiplying by the "right" reciprocal. 

2 7 _ 14 
9 X 3 " 27 

Example 2: Simplify | 4- |. 

Solution: Begin by multiplying by the "right" reciprocal. 

7^2_7 3 _ 7-3 _ 7 
3^3~3 X 2~ 2~^3 " 2 

Instead of the division symbol -f , you may see a large fraction bar. This is seen in the next example. 

2 

Example 3: Simplify j-. 

8 

Solution: The fraction bar separating | and | indicates division. 

2^7 

3^8 



Simplify as in Example 2: 



2 8 _ 16 

3 X 7 ~ 21 



Using Reciprocals to Solve Real- World Problems 

The need to divide rational numbers is necessary for solving problems in physics, chemistry, and manu- 
facturing. The following example illustrates the need to divide fractions in physics. 

Example 4: Newton's Second Law relates acceleration to the force of an object and its mass: a = -. 
ii m 

Suppose F = 7g and m = ^. Find a, the acceleration. 

Solution: Before beginning the division, the mixed number of force must be rewritten as an improper 
fraction. 

Replace the fraction bar with a division symbol and simplify: a= jtJ. 

^ x | = ^ = 36§. Therefore, the acceleration is 36§ m/s 2 . 

Example 5: Anne runs a mile and a half in one-quarter hour. What is her speed in miles per hour? 

Solution: Use the formula speed = &^. 

^ time 

1 
,5 = 1.5-=- T 

4 
Rewrite the expression and simplify: ^=|*x = It = T = ^ m i/hr. 

71 www.ckl2.org 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Division of Rational Numbers (8:20) 




Figure 2.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/734 



1. Define inverse. 

2. What is the multiplicative inverse? How is this different from the additive inverse? 



In 3 - 11, find the multiplicative inverse of each expression. 



3. 100 



4. 


2 
8 


5. 


19 


21 


6. 


7 




^3 


7. 


Z 
2xy 2 


8. 





9. 


1 

3 


10. 


-19 

18 


11. 


3 AT 

~8z 



In 12 - 20, divide the rational numbers. Be sure that your answer in the simplest form. 



12 5,i 

1Z. 2 . 4 

lO. 2 . g 
14. 7 

10. 2 • 2 

16 -- - - 

1U. 2 . 7 

17 - - — 

11 ' 2 • 4y 



is- RM-!) 

19 Z^.7 

i». 2 . 4 

20. ll-(-f) 



In 21 - 23, evaluate the expression. 



21. * /orr 



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and v 



72 



22. 4z + u for u = 0.5 and z = 10 

23. ^ form=l 

m J 5 

24. The label on a can of paint states that it will cover 50 square feet per pint. If I buy a |-pint sample, 
it will cover a square two feet long by three feet high. Is the coverage I get more, less, or the same 
as that stated on the label? 

25. The world's largest trench digger, "Bagger 288," moves at | mph. How long will it take to dig a 
trench |-mile long? 

26. A | Newton force applied to a body of unknown mass produces an acceleration of ^ m/s 2 . Calculate 
the mass of the body. Note: Newton = kg m/s 2 

27. Explain why the reciprocal of a nonzero rational number is not the same as the opposite of that 
number. 

28. Explain why zero does not have a reciprocal. 



Mixed Review 






Simplify. 






29. 199 -(-11) 






30. -2.3 -(-3.1) 






31. |16-84| 

32. |^| 

33. (4^2x6 + 10- 

34. Evaluate f{x) - 

35. Define range. 


-5) 2 

-w- 


-3);/(21) 



2.7 Square Roots and Real Numbers 




Human chess is a variation of chess, often played at Renaissance fairs, in which people take on the roles of 
the various pieces on a chessboard. The chessboard is played on a square plot of land that measures 324 
square meters with the chess squares marked on the grass. How long is each side of the chessboard? 

To answer this question, you will need to know how to find the square root of a number. 

The square root of a number n is any number such that s 2 = n. 

Every positive number has two square roots, the positive and the negative. The symbol used to represent 
the square root is ^fx. It is assumed that this is the positive square root of x. To show both the positive 
and negative values, you can use the symbol ±, read "plus or minus." 

73 www.ckl2.org 



For example: 

V81 = 9 means the positive square root of 81. 

- V81 = -9 means the negative square root of 81. 

± V81 = ±9 means the positive or negative square root of 81. 

Example 1: The human chessboard measures 324 square meters. How long is one side of the square? 

Solution: The area of a square is s 2 = Area. The value of Area can be replaced with 324. 

s 2 = 324 

The value of s represents the square root of 324. 

s= V324= 18 

The chessboard is 18 meters long by 18 meters wide. 

Approximating Square Roots 

When the square root of a number is a whole number, this number is called a perfect square. 9 is a 
perfect square because V9 = 3. 

Not all square roots are whole numbers. Many square roots are irrational numbers, meaning there is no 
rational number equivalent. For example, 2 is the square root of 4 because 2x2 = 4. The number 7 is the 
square root of 49 because 7 x 7 = 49. What is the square root of 5? 

There is no whole number multiplied by itself to equal five, so the V5 is not a whole number. To find the 
value of V5, we can use estimation. 

To estimate the square root of a number, look for the perfect integers less than and greater than the 
value, then estimate the decimal. 

Example 2: Estimate a/5. 

Solution: The perfect square below 5 is 4 and the perfect square above 5 is 9. Therefore, 4 < 5 < 9. 
Therefore, V5 is between V4 and V9, or 2 < V5 < 3. Because 5 is closer to 4 than 9, the decimal is a low 
value. V5 ~ 2.2 

Identifying Irrational Numbers 

Recall the number hierarchy from Lesson 2.1. Real numbers have two categories: rational and irrational. 
If a value is not a perfect square, then it is considered an irrational number. These numbers cannot be 
written as a fraction because the decimal does not end (non-terminating) and does not repeat a pattern 
(non-repeating). Although irrational square roots cannot be written as fractions, we can still write them 
exactly, without typing the value into a calculator. 

For example, suppose you do not have a calculator and you need to find Vl8. You know there is no 
whole number squared that equals 18, so Vl8 is an irrational number. The value is between Vl6 = 4 and 
V25 = 5. However, we need to find an exact value of Vl8. 

Begin by writing the prime factorization of Vl8. Vl8 = V9 X 2 = V9 x y/2. The V9 = 3 but V2 does 
not have a whole number value. Therefore, the exact value of Vl8 = 3 v2. 

You can check your answer in the calculator by finding the decimal approximation for each square root. 
www.ckl2.org 74 



Example 3: Find the exact value V75. 
Solution: 



V75= V25 x 3 = V25x V3 = 5 V3 



Classifying Real Numbers 



Example 4: Using the chart found in Lesson 2.1, categorize the following numbers: 

a) 

b)-l 

c)§ 

d)^ 
Solutions: 

a) Zero is a whole number, an integer, a rational number, and a real number. 

b) -1 is an integer, a rational number, and a real number. 

c) | is an irrational number and a real number. 



d) -4— = I = o. This is a rational number and a real number. 



Graphing and Ordering Real Numbers 

Every real number can be positioned between two integers. Many times you will need to organize real 
numbers to determine the least value, greatest value, or both. This is usually done on a number line. 

Example 5: Plot the following rational numbers on the number line. 



c)| 
d) 5Z 

a ) 16 

Solutions: 

a) I — 0.6, which is between and 1. 



-2 



b) -| is between -1 and 0. 



J_L 



J I 



-1 



4 I I ' ' ' + ' ' 

-2 -1 







1 



++ 



3 ' 



Ml 



f ° 



1 



C ) | * 304159 ^ L5?1 



J_L 



-10 -9 -8 -7 -6-5-4-3-2-1 1 2 3 4 5 

75 



7 8 9 10 



www.ckl2.org 



d) fl = 3.5625 



t i n i iiii I j| 



3 ^~ 



57 
16 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Square Roots and Real Numbers (10:18) 




Figure 2.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/735 

Find the following square roots exactly without using a calculator. Give your answer in the simplest 
form. 



1. 


V25 


2. 


V24 


3. 


V20 


4. 


V200 


5. 


V2000 


6. 


Vt 


7. 


V! 


8. 


V0.16 


9. 


Vol 



io. Vool 



Use a calculator to find the following square roots. Round to two decimal places. 



11. 


Vl3 


12. 


V99 


13. 


V123 


14. 


V2 


15. 


V2000 


16. 


V0.25 


17. 


Vl.35 


18. 


V0.37 


19. 


Voj 


20. 


Vo.oi 


WW 


xkl2.or 



76 



Classify the following numbers. Include all the categories that apply to the number. 

21. VC125 

22. VL35 

23. V20 

24. V25 

25. VlOO 

26. Place the followingz-aumbers in numerical order, from lowest to highest. 

~2~ 50 L5 13 

27. Use the marked points on the number line and identify each proper fraction. 



a be d 



■J-4- 



1 1 1 4 I 4 1 1 1 41 

12 3. 

Mixed Review 

28. Simplify § + 6. 

29. The area of a triangle is given by the formula A — 4p, where b — base of the triangle and h — height 
of the triangle. Determine the area of a triangle with base = 3 feet and height = 7 feet. 

30. Reduce the fraction ^P. 

31. Write a table for the situation: Tracey jumps 60 times per minutes. Let the minutes be {0, 1, 2, 3, 4, 5, 6}. 
What is the range of this function? 

2.8 Problem- Solving Strategies: Guess and Check 
and Work Backwards 

This lesson will expand your toolbox of problem-solving strategies to include guess and check and work 
backwards. Let's begin by reviewing the four-step problem-solving plan. 

Step 1: Understand the problem. 

Step 2: Devise a plan — Translate. 

Step 3: Carry out the plan — Solve. 

Step 4: Look — Check and Interpret. 

Develop and Use the Strategy: Guess and Check 

The strategy for the "guess and check" method is to guess a solution and use that guess in the problem 
to see if you get the correct answer. If the answer is too big or too small, then make another guess that 
will get you closer to the goal. You continue guessing until you arrive at the correct solution. The process 
might sound like a long one; however, the guessing process will often lead you to patterns that you can use 
to make better guesses along the way. 

Here is an example of how this strategy is used in practice. 

Example 1: Nadia takes a ribbon that is 48 inches long and cuts it in two pieces. One piece is three times 
as long as the other. How long is each piece? 

77 www.ckl2.org 



Solution: We need to find two numbers that add to 48. One number is three times the other number. 

Guess 5 and 15 the sum is 5 + 15 = 20 which is too small 

Guess bigger numbers 6 and 18 the sum is 6 + 18 = 24 which is too small 

However, you can see that the previous answer is exactly half of 48. 
Multiply 6 and 18 by two. 

Our next guess is 12 and 36 the sum is 12 + 36 = 48 This is correct. 

Develop and Use the Strategy: Work Backwards 

The "work backwards" method works well for problems in which a series of operations is applied to an 
unknown quantity and you are given the resulting value. The strategy in these problems is to start with 
the result and apply the operations in reverse order until you find the unknown. Let's see how this method 
works by solving the following problem. 

Example 2: Anne has a certain amount of money in her bank account on Friday morning. During the 
day she writes a check for $24-50, makes an ATM withdrawal of $80, and deposits a check for $235. At 
the end of the day, she sees that her balance is $451.25. How much money did she have in the bank at the 
beginning of the day ? 

Solution: We need to find the money in Anne's bank account at the beginning of the day on Friday. From 
the unknown amount, we subtract $24.50 and $80 and we add $235. We end up with $451.25. We need to 
start with the result and apply the operations in reverse. 

Start with $451.25. Subtract $235, add $80, and then add $24.50. 

451.25 - 235 + 80 + 24.50 = 320.75 

Anne had $320.75 in her account at the beginning of the day on Friday. 

Plan and Compare Alternative Approaches to Solving Problems 

Most word problems can be solved in more than one way. Often one method is more straightforward than 
others. In this section, you will see how different problem-solving approaches compare for solving different 
kinds of problems. 

Example 3: Nadia's father is 36. He is 16 years older than four times Nadia's age. How old is Nadia? 

Solution: This problem can be solved with either of the strategies you learned in this section. Let's solve 
the problem using both strategies. 

Guess and Check Method: 

We need to find Nadia's age. 

We know that her father is 16 years older than four times her age, or 4x (Nadia's age) + 16. 

We know her father is 36 years old. 

Work Backwards Method: 

Nadia's father is 36 years old. 

To get from Nadia's age to her father's age, we multiply Nadia's age by four and add 16. 

Working backward means we start with the father's age, subtract 16, and divide by 4. 

www.ckl2.org 78 



Solve Real- World Problems Using Selected Strategies as Part of 
a Plan 

Example 4: Hana rents a car for a day. Her car rental company charges $50 per day and $0.40 per mile. 
Peter rents a car from a different company that charges $10 per day and $0.30 per mile. How many miles 
do they have to drive before Hana and Peter pay the same price for the rental for the same number of 
miles ? 

Solution: Hana's total cost is $50 plus $0.40 times the number of miles. 

Peter's total cost is $70 plus $0.30 times the number of miles. 

Guess the number of miles and use this guess to calculate Hana's and Peter's total cost. 

Keep guessing until their total cost is the same. 



Guess 


50 miles 




Check 


$50 + $0.40(50) = 


= $70 


Guess 


60 miles 




Check 


$50 + $0.40(60) = 


= $74 



$70 + $0.30(50) = $85 



$70 + $0.30(60) = $88 



Notice that for an increase of 10 miles, the difference between total costs fell from $15 to $14. To get the 
difference to zero, we should try increasing the mileage by 140 miles. 



Guess 200 miles 

Check $50 + $0.40(200) = $130 



$70 + $0.30(200) = $130 



correct 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Problem Solving Word Problems 2 (12:20) 




Figure 2.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/736 



1. Finish the problem we started in Example 3. 

2. Nadia is at home and Peter is at school, which is 6 miles away from home. They start traveling toward 
each other at the same time. Nadia is walking at 3.5 miles per hour and Peter is skateboarding at 6 
miles per hour. When will they meet and how far from home is their meeting place? 



79 



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3. Peter bought several notebooks at Staples for $2.25 each and he bought a few more notebooks at 
Rite- Aid for $2 each. He spent the same amount of money in both places and he bought 17 notebooks 
in total. How many notebooks did Peter buy in each store? 

4. Andrew took a handful of change out of his pocket and noticed that he was holding only dimes and 
quarters in his hand. He counted that he had 22 coins that amounted to $4. How many quarters and 
how many dimes does Andrew have? 

5. Anne wants to put a fence around her rose bed that is one and a half times as long as it is wide. She 
uses 50 feet of fencing. What are the dimensions of the garden? 

6. Peter is outside looking at the pigs and chickens in the yard. Nadia is indoors and cannot see the 
animals. Peter gives her a puzzle. He tells her that he counts 13 heads and 36 feet and asks her how 
many pigs and how many chickens are in the yard. Help Nadia find the answer. 

7. Andrew invests $8000 in two types of accounts: a savings account that pays 5.25% interest per year 
and a more risky account that pays 9% interest per year. At the end of the year, he has $450 in 
interest from the two accounts. Find the amount of money invested in each account. 

8. There is a bowl of candy sitting on our kitchen table. This morning Nadia takes one-sixth of the 
candy. Later that morning Peter takes one-fourth of the candy that's left. This afternoon, Andrew 
takes one-fifth of what's left in the bowl and finally Anne takes one-third of what is left in the bowl. 
If there are 16 candies left in the bowl at the end of the day, how much candy was there at the 
beginning of the day? 

9. Nadia can completely mow the lawn by herself in 30 minutes. Peter can completely mow the lawn 
by himself in 45 minutes. How long does it take both of them to mow the lawn together? 

Mixed Review 



10. Rewrite V500 as a simplified square root 

11. To which number categories does ^| belo 

12. Simplify ±|19 - 65| - 14. 



2 

13. Which property is being applied? 16 + 4c + 11 = (16 + 11) + 4c 

14. Is {(4, 2), (4, -2), (9, 3), (9, -3)} a function? 

15. Write using function notation: y = j^x - 5. 

16. Jordyn spent $36 on four cases of soda. How much was each case? 



2.9 Chapter 2 Review 

Compare the real numbers. 

1. 7 and -11 

2. | and ±± 

3. S and | 

4. 0.985 and § 

5. -16.12 and =f^ 

Order the real numbers from least to greatest. 

7 5 



6 A J- o 
u ' 11' 10' 9 

7 2 J_ _8_ 4 

' ' 7' 11' 13' 7' 



Graph these values on the same number line. 
www.ckl2.org 80 



3± 



9 

10. I 

11. 0.16 

12 — 



1.875 



Simplify by applying the Distributive Property. 

13. 6n(-2 + 5w) - n(-3n - 8) 

14. 7x + 2(-6x + 2) 

15. -7x(x + 5) + 3(4x - 8) 

16. -3(-6r-5)-2r(l + 6r) 

17. l + 3(p + 8) 

18. 3(1 - 5ik) - 1 

Approximate the square root to the nearest hundredth. 

19. V26 

20. V330 

21. V625 

22. Vl21 

23. V225 

24. VTl 

25. V8 

Rewrite the square root without using a calculator. 

26. V50 

27. V8 

28. V80 

29. V32 

Simplify by combining like terms. 

30. 8 + b + l-7b 

31. 9n + 9n + 17 

32. 7/1-3 + 3 

33. 9x+ll-x-3 + 5x + 2 

Evaluate. 

34. | - | 



35. 



36. i + l§ 

37. f x 1 

38. I x I 

39. -if x-2| 

40 I ^ _il 

iu. 9 . ± 3 



81 



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41. 


-3 . -10 

2 ; 7 , 


42. 


°10 • Z 4 


43. 


l|-(-3f) 


44. 


4| + 3| 


45. 


5.4 + (-9.7) 


46. 


(-7.1) + (-0.4) 


47. 


(-4.79) + (-3.63) 


48. 


(-8.1) - (-8.9) 


49. 


1.58 -(-13.6) 


50. 


(-13.6) + 12 -(-15.5) 


51. 


(-5.6) - (-12.6) + (-6.6) 


52. 


19.4 + 24.2 


53. 


8.7 + 3.8 + 12.3 


54. 


9.8-9.4 


55. 


2.2 - 7.3 



List all the categories that apply to the following numbers. 



56. 


10.9 


57. 
58. 


-9 
10 

3tt 


59. 
60. 


n jt 
2 2 

-21 


61. 


8 



Which property has been applied? 

62. 6.78 + (-6.78) = 

63. 9.8 + 11.2 + 1.2 = 9.8 + 1.2 + 11.2 

64. 3a + (4a + 8) = (3a + 4a) + 8 

65 - 3 ~{~6) = 3 + 6 

66. (1); = ; 

67. 8(11)(|) = 8(|)(11) 

Solve the real-world situation. 

68. Carol has 18 feet of fencing and purchased an addition 132 inches. How much fencing does Carol 
have? 

69. Ulrich is making cookies for a fundraiser. Each cookie requires |-pound of dough. He has 12 pounds 
of cookie dough. How many cookies can Ulrich make? 

70. Herrick bought 11 DVDs at $19.99 each. Use the Distributive Property to show how Herrick can 
calculate mentally the amount of money he will need. 

71. Bagger 288 is a trench digger, which moves at | miles /hour. How long will it take to dig a trench 14 
miles long? 

72. Georgia started with a given amount of money, a. She spent $4.80 on a large latte, $1.20 on an 
English muffin, $68.48 on a new shirt, and $32.45 for a present. She now has $0.16. How much 
money, a, did Georgia have in the beginning? 

73. The formula for an area of a square is A = s 2 . A square garden has an area of 145 meters 2 . Find the 
length of the garden exactly. 

www.ckl2.org 82 



2.10 Chapter 2 Test 

Simplify by using the Distributive Property. 

1. -3 + 7(3a-2) 

2. 8(3 + 2q) + 5(q + 3) 

Simplify. 



15 



3. 


8p - 5p 


4. 


9z + 33 - 2z - 


5. 


-f-2 


6. 


If X5| 


7. 


1 o2 


8. 


1 , h 

14 + 8 


9. 


3.5 - 5 - 10.4 


10. 


J - (-6.5) x | 



Simplify the square root exactly without a calculator. 



11. V125 

12. Vl8 

13. How is the multiplicative inverse different from the additive inverse? 

14. A square plot of land has an area of 168 miles 2 . To the nearest tenth, what is the length of the land? 

15. Troy plans to equally divide 228 candies by 16 people. Can this be done? Explain your answer. 

16. Laura withdrew $15 from the ATM, wrote a check for $46.78, and deposited her paycheck of $678.12. 
After her deposit she had $1123.45 in her account. How much money did Laura begin with? 

17. Will the area of a circle always be an irrational number? Explain your reasoning. 

18. When would you use the Commutative Property of Multiplication? Give an example to help illustrate 
your explanation. 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. or g/flexr/ 'chapter/ '96 12. 



83 www.ckl2.org 



Chapter 3 
Linear Equations 



Aside from simplifying algebraic expressions and graphing functions, solving equations is one of the most 
important concepts in mathematics. To successfully manipulate an equation, you must understand and be 
able to apply the rules of mathematics. 




Mathematical equations are used in many different career fields. Medical researchers use equations to 
determine the length of time it takes for a drug to circulate throughout the body, botanists use equations 
to determine the amount of time it takes a Sequoia tree to reach a particular height, and environmental 
scientists can use equations to approximate the number of years it will take to repopulate the bison species. 




In this chapter, you will learn how to manipulate linear equations to solve for a particular variable. You 
already have some experience solving equations. This chapter is designed to help formalize the mental 



www.ckl2.org 



84 



math you use to answer questions in daily life. 




3.1 One-Step Equations 

It's Easier than You Think 

You have been solving equations since the beginning of this textbook, although you may not have recognized 
it. For example, in Lesson 1.4, you determined the answer to the pizza problem below. 

$20.00 was one-quarter of the money spent on pizza. 

\m = 20.00 What divided by 4 equals 20.00? 

The solution is 80. So, the amount of money spent on pizza was $80.00. 

By working through this question mentally, you were applying mathematical rules and solving for the 
variable m. 

Definition: To solve an equation means to write an equivalent equation that has the variable by itself 
on one side. This is also known as isolating the variable. 

In order to begin solving equations, you must understand three basic concepts of algebra: inverse operations, 
equivalent equations, and the Addition Property of Equality. 



Inverse Operations and Equivalent Equations 

In Lesson 1.2, you learned how to simplify an expression using the Order of Operations: Parentheses, 
Exponents, Multiplication and Division completed in order from left to right, and Addition and Subtraction 
(also completed from left to right). Each of these operations has an inverse. Inverse operations "undo" 
each other when combined. 

For example, the inverse of addition is subtraction. The inverse of an exponent is a root. 

Example 1: Determine the inverse of division. 

Solution: To undo dividing something, you would multiply. 

By applying the same inverse operations to each side of an equation, you create an equivalent equation. 

Definition: Equivalent equations are two or more equations having the same solution. 

85 www.ckl2.org 



The Addition Property of Equality 

Just like Spanish, chemistry, or even music, mathematics has a set of rules you must follow in order to be 
successful. These rules are called properties, theorems, or axioms. They have been proven or agreed upon 
years ago, so you can apply them to many different situations. 

For example, the Addition Property of Equality allows you to apply the same operation to each side 
of the equation, or "what you do to one side of an equation you can do to the other." 

The Addition Property of Equality 

For all real numbers a, b, and c: 
If a = /?, then a + c = b + c. 

Solving One-Step Equations Using Addition or Subtraction 

Because subtraction can be considered "adding a negative," the Addition Property of Equality also works 
if you need to subtract the same value from each side of an equation. 

Example 2: 

Solve for y: 16 = y - 11. 

Solution: When asked to solve for y, your goal is to write an equivalent equation with the variable y 
isolated on one side. 

Write the original equation 16 = y — 11. 

Apply the Addition Property of Equality 16 + 11 =y-ll + ll 

Simplify by adding like terms 27 = y. 

The solution is y = 27. 

Example 3: One method to weigh a horse is to load it into an empty trailer with a known weight and 
reweigh the trailer. A Shetland pony is loaded onto a trailer that weighs 2,200 pounds empty. The trailer 
is then reweighed. The new weight is 2,550 pounds. How much does the pony weigh? 

Solution: Choose a variable to represent the weight of the pony, say p. 

Write an equation 2550 = 2200 + p. 

Apply the Addition Property of Equality 2550 - 2200 = 2200 + p - 2200. 

Simplify 350 = p. 

The Shetland pony weighs 350 pounds. 

Equations that take one step to isolate the variable are called one-step equations. Such equations can 
also involve multiplication or division. 

Solving One-Step Equations Using Multiplication or Division 

The Multiplication Property of Equality 

For all real numbers a, b, and c: 
If a = b, then a(c) = b(c). 
Example 4: 
Solve for k : -8Jfc = -96. 

www.ckl2.org 86 



Solution: Because —8k = — 8 x &, the inverse operation of multiplication is division. Therefore, we must 
cancel multiplication by applying the Multiplication Property of Equality. 

Write the original equation -8k = -96. 

Apply the Multiplication Property of Equality -8k -f -8 = -96 4- -8. 

The solution is k = 12. 

When working with fractions, you must remember: | X | = 1. In other words, in order to cancel a fraction 
using division, you really must multiply by its reciprocal. 

Example 5: Solve | • x = 1.5. 

The variable x is being multiplied by one-eighth. Instead of dividing two fractions, we multiply by the 
reciprocal of i, which is 8. 



*(H-8<U» 



x= 12 

Solving Real- World Problems Using Equations 

As was mentioned in the chapter opener, many careers base their work on manipulating linear equations. 
Consider the botanist studying bamboo as a renewable resource. She knows bamboo can grow up to 60 
centimeters per day. If the specimen she measured was 1 meter tall, how long would it take to reach 5 
meters in height? By writing and solving this equation, she will know exactly how long it should take for 
the bamboo to reach the desired height. 

Example 6: In good weather, tomato seeds can grow into plants and bear ripe fruit in as few as 19 weeks. 
Lorna planted her seeds 11 weeks ago. How long must she wait before her tomatoes are ready to be picked? 

Solution: The variable in question is the number of weeks until the tomatoes are ready. Call this variable 
w. 

Write an equation w + 11 = 19. 

Solve for w by using the Addition Property of Equality. 

w+11-11 = 19-11 

w = 8 




It will take as few as 8 weeks for the plant to bear ripe fruit. 

87 www.ckl2.org 



Example 7: In 2004, Takeru Kobayashi of Nagano, Japan, ate 53^ hot dogs in 12 minutes. He broke his 
previous world record, set in 2002, by three more hot dogs. Calculate: 

a) How many minutes it took him to eat one hot dog. 

b) How many hot dogs he ate per minute. 

c) What his old record was. 
Solution: 

a) Write an equation, letting m represent the number of minutes to eat one hot dog. Then, 53.5m = 12 
Applying the Multiplication Property of Equality, 

53.5m 12 



53.5 53.5 

m = 0.224 minutes 

It took approximately 0.224 minutes or 13.44 seconds to eat one hot dog. 
Questions b) and c) are left for you to complete in the exercises. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: One-Step Equations (12:30) 




Figure 3.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/739 



Solve for the given variable. 



1. 


x+ll = 7 


2. 


x- 1.1 = 3.2 


3. 


7x = 21 


4. 
5. 
6. 

7. 
8. 


4x = 1 

bx 2 
12 ~~ 3 
X ~ r" q o" 

v 5 - 3 
A 6 — 8 

0.01* = 11 


9. 


4-13 = -13 


10. 


2+1.1 = 3.0001 


11. 


21s = 3 


WW 


xkl2.org 



88 



12. t+\ = \ 



13 



7/ _ 7 



11 — 11 
14 - = -- • v 

15. 6r= | 
1 6 ^ = 3 

1U ' 16 8 

17. Peter is collecting tokens on breakfast cereal packets in order to get a model boat. In eight weeks 
he has collected 10 tokens. He needs 25 tokens for the boat. Write an equation and determine the 
following information. 

(a) How many more tokens he needs to collect, n. 

(b) How many tokens he collects per week, w. 

(c) How many more weeks remain until he can send off for his boat, r. 

18. Juan has baked a cake and wants to sell it in his bakery. He is going to cut it into 12 slices and sell 
them individually. He wants to sell it for three times the cost of making it. The ingredients cost him 
$8.50, and he allowed $1.25 to cover the cost of electricity to bake it. Write equations that describe 
the following statements. 

(a) The amount of money that he sells the cake for (u). 

(b) The amount of money he charges for each slice (c) . 

(c) The total profit he makes on the cake (w). 

19. Solve the remaining two questions regarding Takeru Kobayashi in Example 7. 
Mixed Review 

20. Simplify V48. 

21. Classify 6.23 according to the real number chart. 

22. Reduce ^. 

23. Graph the following ordered pairs: {(2, -2), (4, -1), (5, -5), (3, -2)}. 

24. Define evaluate. 

25. Underline the math verb in this sentence: The difference between m and n is 16. 

26. What property is illustrated here? 4(a + 11.2) = 4(a) + 4(11.2) 



3.2 Two-Step Equations 



Suppose Shaun weighs 146 pounds and wants to lose enough weight to wrestle in the 130-pound class. His 
nutritionist designed a diet for Shaun so he will lose about 2 pounds per week. How many weeks will it 
take Shaun to weigh enough to wrestle in his class? 

This is an example that can be solved by working backward (Lesson 2.8). In fact, you may have already 
found the answer by using this method. The solution is 8 weeks. 

By translating this situation into an algebraic sentence, we can begin the process of solving equations. 
To solve an equation means to "undo" all the operations of the sentence, leaving a value for the variable. 

Translate Shaun's situation into an equation. 

-2w + 146 = 130 

This sentence has two operations: addition and multiplication. To find the value of the variable, we must 
use both properties of Equality: the Addition Property of Equality and the Multiplication Property of 
Equality. 

89 www.ckl2.org 



Procedure to Solve Equations of the Form ax + b = some number: 

1. Use the Addition Property of Equality to get the variable term ax alone on one side of the equation: 

ax = some number 

2. Use the Multiplication Property of Equality to get the variable x alone on one side of the equation: 

x = some number 

Example 1: Solve Shawn's problem. 

Solution: -2w + 146 = 130 

Apply the Addition Property of Equality: -2w + 146 - 146 = 130 - 146. 

Simplify: -2w = -16. 

Apply the Multiplication Property of Equality: -2w -f -2 = -16 -f -2. 

The solution is w = 8. 

It will take 8 weeks for Shaun to weigh 130 pounds. 

Solving Equations by Combining Like Terms 

Michigan has a 6% sales tax. Suppose you made a purchase and paid $95.12, including tax. How much 
was the purchase before tax? 

Begin by determining the noun that is unknown and choose a letter as its representation. 

The purchase price is unknown so this is our variable. Call it p. Now translate the sentence into an 
algebraic equation. 

price + (0.0Q)price = total amount 
/? + 0.06/? = 95.12 

To solve this equation, you must know how to combine like terms. 

Like terms are expressions that have identical variable parts. 

According to this definition, you can only combine like terms if they are identical. Combining like 
terms only applies to addition and subtraction! This is not a true statement when referring to 
multiplication and division. 

The numerical part of an algebraic term is called the coefficient. To combine like terms, you add (or 
subtract) the coefficients of the identical variable parts. 

Example 2: Identify the like terms, then combine. 

10/? + 7bc + 4c + (-8b) 

Solution: Like terms have identical variable parts. The only terms having identical variable parts are 10b 
and -8b. To combine these like terms, add them together. 

10b + 7bc + 4c + -8b = 2b + 7bc + 4c 
You will now apply this concept to the Michigan sales tax situation. 
www.ckl2.org 90 



Example 3: What was the purchase amount from this section's opening scenario? 

Solution: p + 0.06/7 = 95.12 

Combine the like terms: p + 0.06/? = 1.06/?, since p = \p. 

Simplify: 1.06/? = 95.12. 

Apply the Multiplication Property of Equality: 1.06/? -f 1.06 = 95.12 -f 1.06. 

Simplify: p = 89.74. 

The price before tax was $89.74. 

The next several examples show how algebraic equations can be created to solve real- world situations. 




Example 4: An emergency plumber charges $65 as a call-out fee plus an additional $75 per hour. He 
arrives at a house at 9:30 and works to repair a water tank. If the total repair bill is $196.25, at what time 
was the repair completed? 

Solution: Translate the sentence into an equation. The number of hours it took to complete the job is 
unknown, so call it h. 

Write the equation: 65 + 75(A) = 196.25. 

Apply the Addition Property and simplify. 

65 + 75(/z)-65 = 196.25-65 

75(h) = 131.25 

Apply the Multiplication Property of Equality: 75(A) -=- 75 = 131.25 -f 75. 

Simplify: h = 1.75. 

The plumber worked for 1.75 hours, or 1 hour, 45 minutes. Since he started at 9:30, the repair was 
completed at 11:15. 

Example 5: To determine the temperature in Fahrenheit, multiply the Celsius temperature by 1.8 then 
add 32. Determine the Celsius temperature if it is 89° F. 

Solution: Translate the sentence into an equation. The temperature in Celsius is unknown; call it C. 

Write the equation: 1.8C + 32 = 89. 

Apply the Addition Property and simplify. 

1.8C + 32 - 32 = 89 - 32 

1.8C = 57 

Apply the Multiplication Property of Equality: 1.8C -f 1.8 = 57 -f 1.8. 

Simplify: C = 31.67. 

If the temperature is 89°F, then it is 31.67°C. 

91 www.ckl2.org 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Two-Step Equations (13:50) 




Figure 3.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/740 



1. Define like terms. Give an example of a pair of like terms and a pair of unlike terms. 

2. Define coefficient 



In 3 - 7, combine the like terms. 



3. -7jc + 39x 

4. 3x 2 + 21x + 5x+10jc 2 

5. 6xy + 7y + 5x + 9xy 

6. Wab + 9-2ab 

7. -7mn - 2mn 2 - 2mn + 8 

8. Explain the procedure used to solve 



-5y - 9 = 74 



Solve and check your solution. 



9. 1.3* - 0.7* = 12 

10. 6jc- 1.3 = 3.2 

11. 5jk-(3jc + 2) = 1 

12. 4(jc + 3) = 1 

13. 5q-7= | 

15. .-| = | 

16. O.lv + 11 = 

5<?-7 _ 2 
12 — 3 
5(g-7) _ 2 
12 3 

33* - 99 = 



17. 

18. 
19. 
20. 
21. 
22. 
23. 
24. 
25. 



5p - 2 = 32 
14x + 9x = 161 
3m — 1 + 4m = 5 
8x + 3 = 11 
24 = 2x + 6 
66= |jfe 



www.ckl2.org 



92 



26. | = \{a + 2) 

27. 16 = -3d -5 

28. Jayden purchased a new pair of shoes. Including a 7% sales tax, he paid $84.68. How much did his 
shoes cost before sales tax? 

29. A mechanic charges $98 for parts and $60 per hour for labor. Your bill totals $498.00, including 
parts and labor. How many hours did the mechanic work? 

30. An electric guitar and amp set costs $1195.00. You are going to pay $250 as a down payment and 
pay the rest in 5 equal installments. How much should you pay each month? 

31. Jade is stranded downtown with only $10 to get home. Taxis cost $0.75 per mile, but there is an 
additional $2.35 hire charge. Write a formula and use it to calculate how many miles she can travel 
with her money. Determine how many miles she can ride. 

32. Jasmin's dad is planning a surprise birthday party for her. He will hire a bouncy castle and provide 
party food for all the guests. The bouncy castle costs $150 dollars for the afternoon, and the food 
will cost $3.00 per person. Andrew, Jasmin's dad, has a budget of $300. Write an equation to help 
him determine the maximum number of guests he can invite. 

Mixed Review 

33. Trish showed her work solving the following equation What did she do incorrectly? 

c= 18 



34. Write an expression for the following situation: Yoshi had d dollars, spent $65, and earned $12. He 
had $96 left 

35. Find the domain of the following graph. 

36. Is it a function? Explain your answer. 

40 1 



30 



>v 20 



10 



e s 10 

X 

1 _ 15 

2 9 ' 

38. What is the additive identity? 

39. Find the opposite of -4. 1398. 

















/ 








/ 






2 


/ 




1 


4/ 












1 








2 - ^"""^ 









37. Find the difference: 



3.3 Multi-Step Equations 



So far in this chapter you have learned how to solve one-step equations of the form y = ax and two-step 
equations of the form y = ax + b. This lesson will expand upon solving equations to include solving 
multi-step equations and equations involving the Distributive Property. 



93 



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Solving Multi-Step Equations by Combining Like Terms 

In the last lesson, you learned the definition of like terms and how to combine such terms. We will use the 
following situation to further demonstrate solving equations involving like terms. 

You are hosting a Halloween party. You will need to provide 3 cans of soda per person, 4 slices of pizza per 
person, and 37 party favors. You have a total of 79 items. How many people are coming to your party? 

This situation has several pieces of information: soda cans, slices of pizza, and party favors. Translate this 
into an algebraic equation. 

3p + 4p + 37 = 79 

This equation requires three steps to solve. In general, to solve any equation you should follow this 
procedure. 

Procedure to Solve Equations: 

1. Remove any parentheses by using the Distributive Property or the Multiplication Property of Equality. 

2. Simplify each side of the equation by combining like terms. 

3. Isolate the ax term. Use the Addition Property of Equality to get the variable on one side of the equal 
sign and the numerical values on the other. 

4. Isolate the variable. Use the Multiplication Property of Equality to get the variable alone on one side 
of the equation. 

5. Check your solution. 

Example 1: Determine the number of party-goers in the opening example. 

Solution: 3p + Ap + 37 = 79 

Combine like terms: 7p + 37 = 79. 

Apply the Addition Property of Equality: 7p + 37 - 37 = 79 - 37. 

Simplify: 7p = 42. 

Apply the Multiplication Property of Equality: 7p 4- 7 = 42 -f 7. 

The solution is p = 6. 

There are six people coming to the party. 

Solving Multi-Step Equations by Using the Distributive Property 

When faced with an equation such as 2(5x + 9) = 78, the first step is to remove the parentheses. There 
are two options to remove the parentheses. You can apply the Distributive Property or you can apply the 
Multiplication Property of Equality. This lesson will show you how to use the Distributive Property to 
solve multi-step equations. 

Example 2: Solve for x: 2(5x + 9) = 78. 

Solution: Apply the Distributive Property: lOx + 18 = 78. 

Apply the Addition Property of Equality: 10* + 18 - 18 = 78 - 18. 

Simplify: IOjc = 60. 

Apply the Multiplication Property of Equality: lOx -f 10 = 60 4- 10. 

The solution is x = 6. 

www.ckl2.org 94 



Check: Does 10(6) + 18 = 78? Yes, so the answer is correct. 

Example 3: Kashmir needs to fence in his puppy. He will fence in three sides, connecting it to his back 
porch. He wants the run to be 12 feet long and he has 4-0 feet of fencing. How wide can Kashmir make his 
puppy enclosure? 

Solution: Translate the sentence into an algebraic equation. Let w represent the width of the enclosure. 



Solve for w. 



w + w+ 12 = 40 



2w + 12 = 40 
2w+12-12 = 40-12 
2w = 28 
2w -f 2 = 28 -f 2 
w = 14 



The dimensions of the enclosure are 14 feet wide by 12 feet long. 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Multi-Step Equations (15:01) 




Figure 3.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/741 



In 1 - 23, solve the equation. 

1. 3(jc-1)-2(jc + 3) = 

2. 7(w + 20)-w = 5 

3. 9(jc-2) = 3x + 3 

4. 2(5*-i)=f 

5-§M)=§ 

6. 4(v+i) = f 

7. 22 = 2(p + 2) 

8. -(m + 4) = -5 

9. 48 = 4(« + 4) 



95 



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1U ' 5 V 5) 25 

11. -10(b - 3) = -100 

12. 6v + 6(4v+l) = -6 

13. -46 = -4(35 + 4) - 6 

14. 8(1 + 7m) + 6 = 14 

15. = -7(6 + 3&) 

16. 35 = -7(2-x) 

17. -3(3a + 1) - 7a = -35 

18. -2(n+|) = -^ 

20. ^3=9 

21. (c + 3)-2c-(l-3c) = 2 

22. 5m-3[7-(l-2m)] = 

23. /-l + 2/ + /-3 = -4 

24. Find four consecutive even integers whose sum is 244. 

25. Four more than two-thirds of a number is 22. What is the number? 

26. The total cost of lunch is $3.50, consisting of a juice, a sandwich, and a pear. The juice cost 1.5 
times as much as the pear. The sandwich costs $1.40 more than the pear. What is the price of the 
pear? 

27. Camden High has five times as many desktop computers as laptops. The school has 65 desktop 
computers. How many laptops does it have? 

28. A realtor receives a commission of $7.00 for every $100 of a home's selling price. How much was the 
selling price of a home if the realtor earned $5,389.12 in commission? 

Mixed Review 

29. Simplify if X §. 

30. Define evaluate. 

31. Simplify V75. 

32. Solve for m : ^m = 12. 

33. Evaluate: ((-5) - (-7) - (-3)) X (-10). 

34. Subtract: 0.125 - ±. 

3.4 Equations with Variables on Both Sides 

As you may now notice, equations come in all sizes and styles. There are single-step, double-step, and 
multi-step equations. In this lesson, you will learn how to solve equations with a variable appearing on each 
side of the equation. The process you need to solve this type of equation is similar to solving a multi-step 
equation. The procedure is repeated here. 

Procedure to Solve Equations: 

1. Remove any parentheses by using the Distributive Property or the Multiplication Property of Equality. 

2. Simplify each side of the equation by combining like terms. 

3. Isolate the ax term. Use the Addition Property of Equality to get the variable on one side of the equal 
sign and the numerical values on the other. 

4. Isolate the variable. Use the Multiplication Property of Equality to get the variable alone on one side 
of the equation. 

www.ckl2.org 96 



5. Check your solution. 




Karen and Sarah have bank accounts. Karen has a starting balance of $125.00 and is depositing $20 each 
week. Sarah has a starting balance of $43 and is depositing $37 each week. When will the girls have the 
same amount of money? 

To solve this problem, you could use the "guess and check" method. You are looking for a particular week 
in which the bank accounts are equal. This could take a long time! You could also translate the sentence 
into an equation. The number of weeks is unknown so this is our variable, call it w. Now translate this 
situation into an algebraic equation: 

125 + 20w = 43 + 37w 

This is a situation in which the variable w appears on both sides of the equation. To begin to solve for 
the unknown, we must use the Addition Property of Equality to gather the variables on one side of the 
equation. 

Example 1: Determine when Sarah and Karen will have the same amount of money. 

Solution: Using the Addition Property of Equality, move the variables to one side of the equation: 

125 + 20w - 20w = 43 + 37w - 20w 

Simplify: 125 = 43 + 17w 

Solve using the steps from Lesson 3.3. 

125 - 43 = 43 - 43 + 17w 
82 = 17w 

82 - 17 = 17w H- 17 

w « 4.82 

It will take about 4.8 weeks for Sarah and Karen to have equal amounts of money. 

Example 2: Solve for h : 3(h + 1) = llh - 23. 

Solution: First you must remove the parentheses by using the Distributive Property. 

3/z + 3 = 11/z- 23 

Gather the variables on one side. 



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Simplify. 



Solve using the steps from Lesson 3.3. 



3ft - 3ft + 3 = lift - 3ft - 23 



8ft -23 



3 + 23 = 8ft - 23 + 23 
26 = 8ft 

26 -r 8 = 8ft -r 8 
13 

T 



ft 



3.25 



Multimedia Link: Watch this video: http : //www . teachertube . com/viewVideo . php?video_id=55491&# 
38;title=Solving_equations_with_variables_on_both_sides for further information on how to solve 
an equation with a variable on each side of the equation. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Equations with Variables on Both Sides (9:28) 




Figure 3.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/742 



In 1 - 13, solve the equation. 



1. 3(jc-1) = 2(jc + 3) 

2. 7(x + 20) = x + 5 

3. 9(jc-2) = 3* + 3 

4. 2 (a-l) = l(a+l) 

M('+§) = i('-§) 

6. l( v+ !) = 2(f-§) 



y-4 
11 

z _ 
16 



2y+l 



~ 5 3 

2(3z+l) 

9 



www.ckl2.org 



98 



Q X i £ — ( 3 4 +1 ) i 3 
v ' 16 "i" 6 ~~ 9 ^2 

10. 21 + 3/7 = 6-6(1-4/7) 

11. -2x + 8 = 8(1 - 4x) 

12. 3(-5v-4) = -6v-39 

13. -5(5£ + 7) = 25 + 5A: 

14. Manoj and Tamar are arguing about how a number trick they heard goes. Tamar tells Andrew to 
think of a number, multiply it by five, and subtract three from the result. Then Manoj tells Andrew 
to think of a number, add five, and multiply the result by three. Andrew says that whichever way 
he does the trick he gets the same answer. What was Andrew's number? 

15. I have enough money to buy five regular priced CDs and have $6 left over. However, all CDs are on 
sale today for $4 less than usual. If I borrow $2, I can afford nine of them. How much are CDs on 
sale for today? 

16. Jaime has a bank account with a balance of $412 and is saving $18 each week. George has a bank 
account with a balance of $874 and is spending $44 dollars each week. When will the two have the 
same amount of money? 

17. Cell phone plan A charges $75.00 each month and $0.05 per text. Cell phone plan B charges $109 
dollars and $0.00 per text. 

(a) At how many texts will the two plans charge the same? 

(b) Suppose you plan to text 3,000 times per month. Which plan should you choose? Why? 

18. To rent a dunk tank, Modern Rental charges $150 per day. To rent the same tank, Budgetwise 
charges $7.75 per hour. 

(a) When will the two companies charge the same? 

(b) You will need the tank for a 24-hour fund raise-a-thon. Which company should you choose? 

Mixed Review 

19. Solve for t: -12 + t = -20. 

20. Solve for r : 3r - 7r = 32. 

21. Solve for e : 35 = 5(^ + 2). 

22. 25 more than four times a number is 13. What is the number? 

23. Find the opposite of 9^. Write your answer as an improper fraction. 

24. Evaluate {\b\ - a) - (\d\ -a). Let a = 4, b = -6, and d = 5. 

25. Give an example of an integer that is not a counting number. 

Quick Quiz 

1. Determine the inverse of addition. 

2. Solve for w : -4w = 16. 

3. Write an equation to represent the situation and solve. Shauna ran the 400 meter dash in 56.7 
seconds, 0.98 seconds less than her previous time. What was her previous time? 

4. Solve for b : ife + 5 = 9. 

5. Solve for q : 3q + 5 - 4q = 19. 



3.5 Ratios and Proportions 



Ratios and proportions have a fundamental place in mathematics. They are used in geometry, size 
changes, and trigonometry. This lesson expands upon the idea of fractions to include ratios and proportions. 

99 www.ckl2.org 



A ratio is a fraction comparing two things with the same units. 

A rate is a fraction comparing two things with different units. 

You have experienced rates many times: 65 mi /hour, $1.99 /pound, $3.79 /yd 2 . You have also experienced 
ratios. A "student to teacher" ratio shows approximately how many students one teacher is responsible 
for in a school. 

Example 1: The State Dining Room in the White House measures approximately 1^8 feet long by 36 feet 
wide. Compare the length of the room to the width, and express your answer as a ratio. 

Solution: 



48 feet _ 4 
36 feet 3 



The length of the State Dining Room is | the width. 

A proportion is a statement in which two fractions are equal: § = §• 

Example 2: Is | = ^ a proportion? 

Solution: Find the least common multiple of 3 and 12 to create a common denominator. 



2 _ _8_ _6_ 

3 " 12 * 12 



This is NOT a proportion because these two fractions are not equal. 

A ratio can also be written using a colon instead of the fraction bar. 

| = 2 can a l so be read, u a is to b as c is to d v or a : b = c : d. 

The values of a and d are called the extremes of the proportion and the values of b and c are called the 
means. To solve a proportion, you can use the cross products. 

The Cross Products of a Proportion: 

If | = 2-> then ad = be. 



Example 3: Solve | = |. 

Solution: Apply the Cross Products of a Proportion. 



6a = 7(9) 
Qa = 63 



Solve for a. 

a = 10.5 
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Consider the following situation: A train travels at a steady speed. It covers 15 miles in 20 minutes. How 
far will it travel in 7 hours, assuming it continues at the same rate? This is an example of a problem that 
can be solved using several methods, including proportions. 

To solve using a proportion, you need to translate the statement into an algebraic sentence. The key to 
writing correct proportions is to keep the units the same in each fraction. 



miles miles 



miles time 



time 



time 



time 



miles 



You will be asked to solve this problem in the practice set. 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Ratio and Proportion (10:25) 




Figure 3.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/743 

Write the following comparisons as ratios. Simplify fractions where possible. 

1. $150 to $3 

2. 150 boys to 175 girls 

3. 200 minutes to 1 hour 

4. 10 days to 2 weeks 

In 5 - 10, write the ratios as a unit rate. 



101 



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5. 54 hotdogs to 12 minutes 

6. 5000 lbs to 250 in 2 

7. 20 computers to 80 students 

8. 180 students to 6 teachers 

9. 12 meters to 4 floors 

10. 18 minutes to 15 appointments 

11. Give an example of a proportion that uses the numbers 5, 1, 6, and 30 

12. In the following proportion, identify the means and the extremes: ^ = || 

In 13 - 23, solve the proportion. 



13. 


13 5 
6 — x 


14. 


1.25 3.6 


J ~~ •* 


15. 


6 x 
19 — 11 


16. 


1 _ 0.01 

x 5 


17. 


300 _ x 
4 99 


18. 


2.75 x 
9 ~(S) 


19. 


1.3 x 


4 ~~ 1.3 


20. 


0.1 1.9 


1.01 ~~ x 


21. 


5p 3 
12 — 11 


22. 


9 4 
x~ 11 


23. 


n+1 _ o 
11 — Z 


24. 


A restaurant serves 100 people per day and takes in $908. If the restaurant were to serve 250 people 



per day, what might the cash collected be? 

25. The highest mountain in Canada is Mount Yukon. It is ^P the size of Ben Nevis, the highest peak 
in Scotland. Mount Elbert in Colorado is the highest peak in the Rocky Mountains. Mount Elbert 
is ^ the height of Ben Nevis and || the size of Mont Blanc in France. Mont Blanc is 4800 meters 
high. How high is Mount Yukon? 

26. At a large high school, it is estimated that two out of every three students have a cell phone, and 
one in five of all students have a cell phone that is one year old or less. Out of the students who own 
a cell phone, what proportion own a phone that is more than one year old? 

27. The price of a Harry Potter Book on Amazon.com is $10.00. The same book is also available used 
for $6.50. Find two ways to compare these prices. 

28. To prepare for school, you purchased 10 notebooks for $8.79. How many notebooks can you buy for 
$5.80? 

29. It takes 1 cup mix and | cup water to make 6 pancakes. How much water and mix is needed to 
make 21 pancakes? 

30. Ammonia is a compound consisting of a 1:3 ratio of nitrogen and hydrogen atoms. If a sample 
contains 1,983 hydrogen atoms, how many nitrogen atoms are present? 

31. The Eagles have won 5 out of their last 9 games. If this trend continues, how many games will they 
have won in the 63-game season? 

32. Solve the train situation described earlier in this lesson. 

Mixed Review 

33. Solve ±§-r§. 

34. Evaluate |9 - 108|. 

35. Simplify: 8(8 - 3x) - 2(1 + 8x). 

36. Solve for n : 7{n + 7) = -7. 

www.ckl2.org 102 



37. Solve for x : -22 = -3 + x. 

38. Solve for u : 18 = 2k. 

39. Simplify: -±-(-l±). 

40. Evaluate: 5 X ||n| when n = 10 and p = -6. 

41. Make a table for -4 < x < 4 /or /(*) = |jc + 2. 

42. Write as an English phrase: y + 11. 



3.6 Scale and Indirect Measurement 

We are occasionally faced with having to make measurements of things that would be difficult to measure 
directly: the height of a tall tree, the width of a wide river, the height of the moon's craters, even the 
distance between two cities separated by mountainous terrain. In such circumstances, measurements can 
be made indirectly, using proportions and similar triangles. Such indirect methods link measurement 
with geometry and numbers. In this lesson, we will examine some of the methods for making indirect 
measurements. 




wL.* ?* vSFTT^^ 



UKRAINE 

f **t '■■■■■■!.■ My\u\JniV 



\ J. FRANCE 



i 



y"*T SKA in '...i.-u. 

,S(V1IU 



MOROCfO 




A map is a two-dimensional, geometrically accurate representation of a section of the Earth's surface. Maps 
are used to show, pictorially, how various geographical features are arranged in a particular area. The scale 
of the map describes the relationship between distances on a map and the corresponding distances on the 
earth's surface. These measurements are expressed as a fraction or a ratio. 

In the last lesson, you learned the different ways to write a ratio: using the fraction bar, using a colon, and 
in words. Outside of mathematics books, ratios are often written as two numbers separated by a colon (:). 
Here is a table that compares ratios written in two different ways. 

Table 3.1: 



Ratio 



Is Read As 



Equivalent To 



1:20 



one to twenty 



m 



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Table 3.1: (continued) 



Ratio Is Read As Equivalent To 

2:3 two to three (§) 

1:1000 one to one-thousand (nToo) 

If a map had a scale of 1:1000 ("one to one-thousand"), one unit of measurement on the map (1 inch or 1 
centimeter, for example) would represent 1000 of the same units on the ground. A 1:1 (one to one) map 
would be a map as large as the area it shows! 




^"*fiifci«rniri 



Example : Anne is visiting a friend in London and is using the map above to navigate from Fleet Street 
to Borough Road. She is using a 1:100,000 scale map, where 1 cm on the map represents 1 km in real life. 
Using a ruler, she measures the distance on the map as 8.8 cm. How far is the real distance from the start 
of her journey to the end? 

The scale is the ratio of distance on the map to the corresponding distance in real life and can be written 
as a proportion. 

dist.on map 1 



realdist. 100,000 



By substituting known values, the proportion becomes: 

8.8 cm 1 



Cross multiply. 



real dist.(x) 100,000 
880000 cm = x 100 cm = 1 m. 

x = 8800 m 1000 m = 1 km. 

The distance from Fleet Street to Borough Road is 8800 m or 8.8 km. 

We could, in this case, use our intuition: the 1 cm = 1 km scale indicates that we could simply use our 
reading in centimeters to give us our reading in km. Not all maps have a scale this simple. In general, you 
will need to refer to the map scale to convert between measurements on the map and distances in real life! 

Example 1: Oscar is trying to make a scale drawing of the Titanic, which he knows was 883 feet long. 
He would like his drawing to be 1:500 scale. How long, in inches, must his sheet of paper be? 

www.ckl2.org 104 



Solution: We can reason that since the scale is 1:500 that the paper must be fljj = 1.766 feet long. 
Converting to inches gives the length at 12(1.766) in = 21.192 in. 

The paper should be at least 22 inches long. 

Not everything has a scale. Architecture such as the St. Louis Arch, St. Basil's Cathedral, or the Eiffel 
Tower does not have a scale written on the side. It may be necessary to measure such buildings. To do so 
requires knowledge of similar figures and a method called indirect measurement. 

Similar figures are often used to make indirect measurements. Two shapes are said to be similar if 
they are the same shape and "in proportion." The ratio of every measurable length in one figure to the 
corresponding length in the other is the same. Similar triangles are often used in indirect measurement. 




Anatole is visiting Paris, and wants to know the height of the Eiffel Tower. Since he's unable to speak 
French, he decides to measure it in three steps. 

1. He measures out a point 500 meters from the base of the tower, and places a small mirror flat on the 
ground. 

2. He stands behind the mirror in such a spot that standing upright he sees the top of the tower reflected 
in the mirror. 

3. He measures both the distance from the spot where he stands to the mirror (2.75 meters) and the 
height of his eyes from the ground (1.8 meters). 

Explain how Anatole is able to determine the height of the Eiffel Tower from these numbers and determine 
what that height is. 

First, we will draw and label a scale diagram of the situation. 




1.8 rr 



500 m 



2.75 m 



The Law of Reflection states, "The angle at which the light reflects off the mirror is the same as the angle 
at which it hits the mirror." Using this principle and the figure above, you can conclude that these triangles 
are similar with proportional sides. 

This means that the ratio of the long leg in the large triangle to the length of the long leg in the small 
triangle is the same ratio as the length of the short leg in the large triangle to the length of the short leg 
in the small triangle. 



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500 m 



1.8 



2.75 m 1.8 m 
500 _ x 

327.3 « jc 



1.8 



The Eiffel Tower, according to this calculation, is approximately 327.3 meters high. 

Example 2: Bernard is looking at a lighthouse and wondering how high it is. He notices that it casts a 
long shadow, which he measures at 200 meters long. At the same time, he measures his own shadow at 3. 1 
meters long. Bernard is 1.9 meters tall. How tall is the lighthouse? 




Solution: Begin by drawing a scale diagram. 

You can see there are two right triangles. The angle at which the sun causes the shadow from the lighthouse 
to fall is the same angle at which Bernard's shadow falls. We have two similar triangles, so we can again 
say that the ratio of the corresponding sides is the same. 




1.9 m 




200 m 



1.9 



3.1 m 

200 m 

3.1 m 
200 m 

3.1 m 

122.6 



1.9 m 
x 

1.9 m 



1.9 



The lighthouse is approximately 122.6 meters tall. 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Scale and Indirect Measurement (10:44) 



www.ckl2.org 



106 




Figure 3.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/744 



1. Define similar figures. 

2. What is true about similar figures? 

3. What is the process of indirect measurement? When is indirect measurement particularly useful? 

4. State the Law of Reflection. How does this law relate to similar figures? 

5. A map has a 1 inch : 20 mile scale. If two cities are 1,214 miles apart, how far apart would they be 
on this map? 

6. What would a scale of 1 mile : 1 mile mean on a map? What problems would the cartographer 
encounter? 

7. A woman 66 inches tall stands beside a tree. The length of her shadow is 34 inches and the length 
of the tree's shadow is 98 inches. To the nearest foot, how tall is the tree? 




8. Use the scale diagram above to determine: 

(a) The length of the helicopter (cabin to tail) 

(b) The height of the helicopter (floor to rotors) 

(c) The length of one main rotor 

(d) The width of the cabin 

(e) the diameter of the rear rotor system 

107 



www.ckl2.org 



9. On a sunny morning, the shadow of the Empire State Building is 600 feet long. At the same time, 
the shadow of a yardstick (3 feet long) is 1 foot, h\ inches. How high is the Empire State building? 

10. Omar and Fredrickson are 12.4 inches apart on a map with a scale of 1.2 inches : 15 miles. How far 
apart are their two cities in miles? 

11. A man 6 feet tall is standing next to a dog. The man's shadow is 9 feet and the dog's shadow is 6 
feet. How tall is the dog? 

12. A model house is 12 inches wide. It was built with a ratio of 3 inches : 4 meters. How wide is the 
actual house? 

13. Using the diagram below and assuming the two triangles are similar, find DE, the length of segment 
DE. 

.A 



AB = 3 



BC=4 CD =2 

14. A 42.9-foot flagpole casts a 253.1-foot shadow. What is the length of the shadow of a woman 5 feet 
5 inches standing next to the flagpole? 

Mixed Review 

15. Solve for n: -(7 - 7a) + 4a = -23 + 3a. 

16. How is evaluating different from solving? Provide an example to help you illustrate your explanation. 

17. Simplify V243. 

18. Simplify: 2(8g + 2) - 1 + 4g - (2 - 5g). 

19. Draw a graph that is not a function. Explain why your picture is not a function. 

20. Jose has | the amount of money that Chloe has. Chloe has four dollars less than Huey. Huey has 
$26. How much does Jose have? 




3.7 Percent Problems 



A percent is a ratio whose denominator is 100. Before we can use percents to solve problems, let's review 
how to convert percents to decimals and fractions and vice versa. 

To convert a decimal to a percent, multiply the decimal by 100. 

Example: Convert 0.3786 to a percent. 



0.3786 x 100 = 37. 



To convert a percentage to a decimal, divide the percentage by 100. 
Example: Convert 98.6% into a decimal. 

98.6 -f 100 = 0.986 



When converting fractions to percents, we can substitute -^ for jc%, where x is the unknown 
Example: Express | as a percent. 



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108 



We start by representing the unknown as x% or y^g. 
'3\ x 



I - I = Cross multiply. 

\5/ 100 



5x =100-3 

5x = 300 

x = = 60 Divide both sides by 5 to solve for x. 

5 J 



(§)=«« 



Now that you remember how to convert between decimals and percents, you are ready for the Percent 
Equation. 

The Percent Equation 

part = % rate X base 

The key words in a percent equation will help you translate it into a correct algebraic equation. Remember 
the equal sign symbolizes the word "is" and the multiplication symbol symbolizes the word "of." 

Example 1: Find 30% of 85. 

Solution: You are asked to find the part of 85 that is 30%. First, translate into an equation. 

n = 30% x 85 

Convert the percent to a decimal and simplify. 

n = 0.30 x 85 
?z = 25.5 

Example 2: 50 is 15% of what number? 
Solution: Translate into an equation. 

50 = 15% xw 

Rewrite the percent as a decimal and solve. 

50 = 0.15 xw 
50 0.15 xw 



0.15 0.15 

333- = w 
3 

For more help with the percent equation, watch this 4-minute video recorded by Ken's MathWorld. How 
to Solve Percent Equations (4:10) 

109 www.ckl2.org 




Figure 3.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/745 



Finding the Percent of Change 



A useful way to express changes in quantities is through percents. You have probably seen signs such as 
"20% more free," or "save 35% today." When we use percents to represent a change, we generally use the 
formula: 



/final amount - original amount \ _ 

Percent change = x 100% 

original amount / 



A positive percent change would thus be an increase, while a negative change would be a decrease. 

Example 3: A school of 500 students is expecting a 20% increase in students next year. How many 
students will the school have? 

Solution: Using the percent of change equation, translate the situation into an equation. Because the 
20% is an increase, it is written as a positive value. 



Percent change = 



final amount - original amount \ 
original amount / 



/final amount - 500 \ 

= ' 500 ' : " ' ; ' 



„ « x ~ 500 

0.2 = 

500 

100 = x- 500 
600 = x 



Divide both sides by 100%. 
Let x = final amount. 
Multiply both sides by 500. 
Add 500 to both sides. 



The school will have 600 students next year. 

Example 4: A $150 mp3 player is on sale for 30% off. What is the price of the player? 

Solution: Using the percent of change equation, translate the situation into an equation. Because the 
30% is a discount, it is written as a negative. 



Percent change = 



final amount - original amount \ 



original amount 






x 100% 



www.ckl2.org 



no 



I x — 150\ 

I I • 100% = -30% Divide both sides by 100%. 

Ix — 150\ 

I j = -0.3% Multiply both sides by 150. 

x - 150 = 150(-0.3) = -45 Add 150 to both sides. 

x = -45 + 150 
x= 105 

The mp3 player will cost $105. 

Many real situations involve percents. Consider the following. 

In 2004, the US Department of Agriculture had 112,071 employees, of which 87,846 were Caucasian. 
Of the remaining minorities, African- American and Hispanic employees had the two largest demographic 
groups, with 11,754 and 6899 employees respectively.* 

a) Calculate the total percentage of minority (non-Caucasian) employees at the USDA. 

b) Calculate the percentage of African- American employees at the USDA. 

c) Calculate the percentage of minority employees at the USDA who were neither African- American nor 
Hispanic. 

a) Use the percent equation RatexTotal = Part. The total number of employees is 112,071. We know that 
the number of Caucasian employees is 87,846, which means that there must be (112, 071-87, 846) = 24, 225 
non-Caucasian employees. This is the part. 

Rate x 112, 071 = 24, 225 Divide both sides by 112, 071. 

Rate « 0.216 Multiply by 100 to obtain percent. 

Rate « 21.6% 

Approximately 21.6% of USDA employees in 2004 were from minority groups. 

b) Total = 112,071 Part = 11,754 

Rate x 112, 071 = 11, 754 Divide both sides by 112, 071. 

Rate « 0.105 Multiply by 100 to obtain percent. 

Rate « 10.5% 

Approximately 10.5% of USDA employees in 2004 were African- American. 

c) We now know there are 24,225 non-Caucasian employees. That means there must be (24, 225 - 11, 754- 
6899) = 5572 minority employees who are neither African- American nor Hispanic. The part is 5572. 

Rate x 112, 071 = 5572 Divide both sides by 112, 071. 

Rate « 0.05 Multiply by 100 to obtain percent. 

Rate * 5% 

Approximately 5% of USDA minority employees in 2004 were neither African- American nor Hispanic. 

Ill www.ckl2.ore; 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Percent Problems (14:15) 




Figure 3.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/747 

Express the following decimals as percents. 

1. 0.011 

2. 0.001 

3. 0.91 

4. 1.75 

5. 20 

Express the following fractions as a percent (round to two decimal places when necessary). 



6. 



10 ±2 

1U ' 97 



Express the following percentages as reduced fractions. 

11. 11% 

12. 65% 

13. 16% 

14. 12.5% 

15. 87.5% 

Find the following. 



16. 32% of 600 is what number? 

17. |% of 16 is what number? 

18. 9.2% of 500 is what number 

19. 8 is 20% of what number? 

20. 99 is 180% of what number? 



www.ckl2.org 



112 



21. What percent of 7.2 is 45? 

22. What percent of 150 is 5? 

23. What percent of 50 is 2500? 

24. A Realtor earns 7.5% commission on the sale of a home. How much commission does the Realtor 
make if the home sells for $215,000? 

25. The fire department hopes to raise $30,000 to repair a fire house. So far the department has raised 
$1,750.00. What percent is this of their goal? 

26. A $49.99 shirt goes on sale for $29.99. By what percent was the shirt discounted? 

27. A TV is advertised on sale. It is 35% off and has a new price of $195. What was the pre-sale price? 

28. An employee at a store is currently paid $9.50 per hour. If she works a full year, she gets a 12% pay 
raise. What will her new hourly rate be after the raise? 

29. Store A and Store B both sell bikes, and both buy bikes from the same supplier at the same prices. 
Store A has a 40% mark-up for their prices, while store B has a 90% mark-up. Store B has a 
permanent sale and will always sell at 60% off those prices. Which store offers the better deal? 

30. 788 students were surveyed about their favorite type of television show. 18% stated that their favorite 
show was reality-based. How many students said their favorite show was reality-based? 

Mixed Review 

31. List the property used at each step of solving the following equation: 

4(jc-3) = 20 

4jc - 12 = 20 

4x = 32 

x = 8 

32. The volume of a cylinder is given by the formula Volume = nr 2 h, where r = radius and h = height of 
the cylinder. Determine the volume of a soup can with a 3- inch radius and a 5. 5- inch height. 

33. Circle the math noun in this sentence: Jerry makes holiday baskets for his youth group. He can make 
one every 50 minutes. How many baskets can Jerry make in 25 hours? 

34. When is making a table a good problem-solving strategy? When may it not be such a good strategy? 

35. Solve for w: ±2 = ^. 

3.8 Problem- Solving Strategies: Use a Formula 

Some problems are easily solved by applying a formula, such as the Percent Equation or the area of a 
circle. In this lesson, you will include using formulas in your toolbox of problem-solving strategies. 

An architect is designing a room that is going to be twice as long as it is wide. The total square footage of 
the room is going to be 722 square feet. What are the dimensions in feet of the room? 



Cl 



Total Area 
= 722 sq.ft. 



■ Length = 2 x width ► 

113 www.ckl2.org 



This situation applies very well to a formula. The formula for the area of a rectangle is: A = /(w), where / = 
length and w = width. From the situation, we know the length is twice as long as the width. Translating 
this into an algebraic equation, we get: 



A = (2w)w 



Simplifying the equation: A = 2w 2 
Substituting the known value for A: 722 = 2w 2 



2w 2 = 722 
w 2 = 361 
w = V361 



Divide both sides by 2. 

Take the square root of both sides. 



19 



2w = 2 x 19 = 38 
w= 19 

The width is 19 feet and the length is 38 feet. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Word Problem Solving 3 (11:06) 




Figure 3.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/748 



1. Patricia is building a sandbox for her daughter. It's going to be five feet wide and eight feet long. 
She wants the height of the sandbox to be four inches above the height of the sand. She has 30 cubic 
feet of sand. How high should the sandbox be? 

2. A 500-sheet stack of copy paper is 1.75 inches high. The paper tray on a commercial copy machine 
holds a two-foot-high stack of paper. Approximately how many sheets is this? 

3. It was sale day at Macy's and everything was 20% less than the regular price. Peter bought a pair 
of shoes, and using a coupon, got an additional 10% off the discounted price. The price he paid for 
the shoes was $36. How much did the shoes cost originally? 

4. Peter is planning to show a video file to the school at graduation, but he's worried that the distance 
the audience sits from the speakers will cause the sound and the picture to be out of sync. If the 
audience sits 20 meters from the speakers, what is the delay between the picture and the sound? 
(The speed of sound in air is 340 meters per second). 



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114 



5. Rosa has saved all year and wishes to spend the money she has on new clothes and a vacation. She 
will spend 30% more on the vacation than on clothes. If she saved $1000 in total, how much money 
(to the nearest whole dollar) can she spend on the vacation? 

6. On a DVD, data is stored between a radius of 2.3 cm and 5.7 cm. Calculate the total area available 
for data storage in square cm. 

7. If a Blu-ray ™ DVD stores 25 gigabytes (GB), what is the storage density, in GB per square cm ? 

8. The volume of a cone is given by the formula Volume = — ^ , where r = radius, and h = height of 
cone. Determine the amount of liquid a paper cone can hold with a 1.5-inch diameter and a 5-inch 
height. 

9. Consider the conversion 1 meter = 39.37 inches. How many inches are in a kilometer? (Hint: A 
kilometer is equal to 1,000 meters) 

10. Yanni's motorcycle travels 108 miles/hour. 1 mph = 0.44704 meters /second. How many meters did 
Yanni travel in 45 seconds? 

11. The area of a rectangle is given by the formula A = l(w). A rectangle has an area of 132 square 
centimeters and a length of 11 centimeters. What is the perimeter of the rectangle? 

12. The surface area of a cube is given by the formula: SurfaceArea = 6x 2 , where x = side of the cube. 
Determine the surface area of a die with a 1-inch side length. 

Mixed Review 

13. Write the ratio in simplest form: 14:21. 

14. Write the ratio in simplest form: 55:33. 

15. Solve for a : ^ = f| . 

16. Solve for x: i^ =^±1, 

17. Solve for y : 4(jc - 7) + x = 2. 

18. What is 24% of 96? 

19. Find the sum: 4§ - (-|). 



3.9 Chapter 3 Review 

Solve for the variable. 



1. 


a + 11.2 = 7.3 


2. 


9.045 + ;' = 27 


3. 


ll = Z>+§ 


4. 


-22 = -3 + £ 


5. 


-9 = n - 6 


6. 


-6 + /= -27 


7. 


f = "18 


8. 
9. 


29 — — 
M ^-66 = 11 


10. 


-5/ = -110 


11. 


76 = -19p 


12. 
13. 
14. 


-h = -9 

q+l _ 9 
11 — Z 

-2 - 2m = -22 


15. 


-5 + | = -7 


16. 


32 = 2b - 3b + 5b 



115 www.ckl2.org 



17. 9 = Ah + Uh 

18. u-3u-2u= 144 

19. 2/ + 5 -7/= 15 

20. -10 = *+ 15-4* 

21. ±Jfc-16 + 2±Jfc = 

99 -1543 _ 3 r - 11 / 11 r - 8\ 

zz " 120 ~~ 5 A "•" 4 V 5 A "•" 5/ 

23. -5.44jc + 5.11(7.3* + 2) = -37.3997 + 6.8x 

24. -5(5r + 7) = 25 + 5r 

25. -7/? + 37 = 2(-6/? + l) 

26. 3(-5y-4) = -6y - 39 

27. 5(a-7) + 2(fl-3(fl-5)) = 

Write the following comparisons as ratios. Simplify when appropriate. 

28. 10 boys to 25 students 

29. 96 apples to 42 pears 

30. $600 to $900 

31. 45 miles to 3 hours 

Write the following as a unit rate. 

32. $4.99 for 16 ounces of turkey burger 

33. 40 computers to 460 students 

34. 18 teachers to 98 students 

35. 48 minutes to 15 appointments 

Solve the proportion. 



36. Solve for n 

37. Solve for x 

38. Solve for b 

39. Solve for n 



6 _ 2 

n—7 n-\-l ' 

_9 _ x-7 

5 — jc+10' 
5b _ S_ 

12 ~ 11' . 
_12 5 

n 2rc+6 ' 

Write the decimal as a percent. 

40. 0.4567 

41. 2.01 

42. 0.005 

43. 0.043 

Write each percent as a decimal. 

44. 23.5% 

45. 0.08% 

46. 0.025% 

47. 125.4% 

Write each percent as a fraction. 

www.ckl2.org 116 



48. 78% 

49. 11.2% 

50. 10.5% 

51. 33.3% 

Solve using the Percent Equation. 

52. 32.4 is 45% of what number? 

53. 58.7 is what percent of 1,000? 

54. What is 12% of 78? 

55. The original price is $44 and the mark-up is 20%. What is the new price? 

56. An item originally priced $240 has a 15% discount. What is the new price? 

57. A pair of shoes originally priced $89.99 is discounted to $74.99. What is the percent of mark-down? 

58. A salon's haircut rose in price from $10 to $14. What is the percent of mark-up? 

59. An item costing c dollars decreased $48, resulting in a 30% mark-down. What was the original price? 

60. The width of a rectangle is 15 units less than its length. The perimeter of the rectangle is 98 units. 
What is the rectangle's length? 

61. George took a cab from home to a job interview. The cab fare was $4.00 plus $0.25 per mile. His 
total fare was $16.75. How many miles did he travel? 

62. The sum of twice a number and 38 is 124. What is the number? 

63. The perimeter of a square parking lot is 260 yards. What are the dimensions of the parking lot? 

64. A restaurant charges $3.79 for - of a pie. At this rate, how much does the restaurant charge for the 
entire pie? 

65. A 60-watt light bulb consumes 0.06 kilowatts /hour of energy. How long was the bulb left on if it 
consumed 5.56 kilowatts /hour of energy? 

66. A 6^-foot-tall car casts a 33.2-foot shadow. Next to the car is an elephant casting a 51.5-foot shadow. 
How tall is the elephant? 

67. Two cities are 87 miles apart. How far would they be on a map with a scale of 5 inches : 32 miles? 



3.10 Chapter 3 Test 



1. School lunch rose from $1.60 to $2.35. What was the percent of mark-up? 

2. Solve for c : f = 11. 

3. Write 6.35 as a percent. 

4. Write the following as a simplified ratio: 85 tomatoes to 6 plants. 

5. Yvonne made 12 more cupcakes than she did yesterday. She made a total of 68 cupcakes over the 
two days. How many cupcakes did she make the second day? 

6. A swing set 8 feet tall casts a 4-foot-long shadow. How long is the shadow of a lawn gnome 4 feet 
tall? 

7. Solve the proportion: ^ = ~|* 

8. Find the distance between Owosso and Perry if they are 16 cm on a map with a scale of 21 km : 4 
cm. 

9. Solve for j : -If - § (f;_ f) = -If 

10. Solve for m : 2m(2 - 4) + 5m(-8) = 9. 

11. Job A pays $15 plus $2.00 per hour. Job B pays $3.75 per hour. When will the two jobs pay exactly 
the same? 

12. Solve for k: 9.0604 + 2.062* = 0.3(2.2* + 5.9). 

13. Solve for a : -9 - a — 15. 

14. 46 tons is 11% of what? 

117 www.ckl2.org 



15. 17% of what is 473 meters? 

16. Find the percent of change from 73 to 309. 

17. JoAnn wants to adjust a bread recipe by tripling its ingredients. If the recipe calls for 4^ cups of 
pastry flour, how much should she use? 

18. A sweater originally marked $80.00 went on sale for $45. What was the percent of change? 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/flexr/chapter/9613. 



www.ckl2.org 118 



Chapter 4 

Graphing Linear Equations and 
Functions 



The ability to graph linear equations and functions is important in mathematics. In fact, graphing equations 
and solving equations are two of the most important concepts in mathematics. If you master these, all 
mathematical subjects will be much easier, even Calculus! 

This chapter focuses on the visual representations of linear equations. You will learn how to graph lines 
from equations and write functions of graphed lines. You will also learn how to find the slope of a line and 
how to use a slope to interpret a graph. 

Weather, such as temperature and the distance of a thunderstorm can be predicted using linear equations. 
You will learn about these applications and more in this chapter. 




4.1 The Coordinate Plane 

In Lesson 1.6, you graphed ordered pairs. This lesson will expand upon your knowledge of graphing ordered 
pairs to include vocabulary and naming of specific items related to ordered pairs. 

An ordered pair is also called a coordinate. The y— value is called the ordinate and the x— value is called 
the abscissa. 

A two-dimensional (2-D) coordinate has the form (x,y). 

The 2-D plane that is used to graph coordinates or equations is called a Cartesian plane or a coordinate 

119 www.ckl2.org 



plane. This 2-D plane is named after its creator, Rene Descartes. The Cartesian plane is separated into 
four quadrants by two axes. The horizontal axis is called the x-axis and the vertical axis is called the 
y-axis. The quadrants are named using Roman Numerals. The image below illustrates the quadrant 
names. 





















Vi 


L 








































U 




















































































IS" 










































































i 


1 








o ■ 












I 




















1 


1 








A 












I 






























*4 










































1 










































^. 
































10 -ft -fi -jd 


\ -*> 


? a fi a m x 




















n 




































^ 










































A 
































1 


1 








■4 










I 


\ i 




















1 


1 








c 










I 


V 






























u 










































8 


















































































-1 


n^ 

























The first value of the ordered pair is the x-value. This value moves along the x-axis (horizontally). The 
second value of the ordered pair is the y-value. This value moves along the y-axis (vertically). This 
ordered pair provides the direction of the coordinate. 

Multimedia Link: For more information on the Cartesian plane and how to graph ordered pairs, visit 
Purple Math's - http://www.purplemath.com/modules/plane.htm - website. 

Example 1: Find the coordinates of points Q and R. 



Vi 


i 
















* ■ 




































■1 . 


































X 


1 

1 . 




; 


i : 


' 


\ I 


6 


I I 


r 


o . 


















-£- 






c 


3 


F 


% 






-■5 ' 

-4- 



















Solution: In order to get to Q, we move three units to the right, in the positive x direction, then two 
units down, in the negative y direction. The x coordinate of Q is +3; the y coordinate of Q is -2. 

G = (3,-2) 

The coordinates of R are found in a similar way. The x-coordinate is +5 (five units in the positive x 
direction). The y-coordinate is -2 (two units in the negative y direction). 



www.ckl2.org 



R= (5,-2). 

120 



Words of Wisdom from the Graphing Plane 



Not all axes will be labeled for you. There will be many times you are required to label your own axes. 
Some problems may require you to graph only the first quadrant. Others need two or all four quadrants. 
The tic marks do not always count by ones. They can be marked in increments of 2, 5, or even ^. The 
axes do not even need to have the same increments! The Cartesian plane below shows an example of this. 

The increments by which you count your axes should MAXIMIZE the clarity of the graph. 



-2 

.1 7E, 
















-15 






C 










_ 1 


























• 
B 




1 
































- n 0£ 








< 


> 

A 






-U.ZD 

E 

•-^ — i 

















0.5 1 1.5 2 2.5 3 3.5 
In Lesson 1.6, you learned the vocabulary words relation, function, domain, and range. 
A relation is a set of ordered pairs. 

A function is a relation in which every x-coordinate matches with exactly one y-coordinate. 
The set of all possible x-coordinates is the domain. 
The set of all possible y-coordinates is called the range. 



Graphing Given Tables and Rules 



If you kept track of the amount of money you earned for different hours of babysitting, you created a 
relation. You can graph the information in this table to visualize the relationship between these two 
variables. 



121 



www.ckl2.org 



Amount of Money at Different Hours of Babysitting 



< 























54 


















48 




















1 


► 






































3 


G 
















3 

I 



I 




















1 


r 


































i 


12 


1 

i 


5 
> 








0- 













5 


10 12 
Number of hours 


16 


18 










Hours 


4 




5 


10 


12 


16 


18 


Total $ 


12 




15 


30 


36 


48 


54 



The domain of the situation would be all positive real numbers. You can babysit for a fractional amount 
of time but not a negative amount of time. The domain would also be all positive real numbers. You 
can earn fractional money, but not negative money. 

If you read a book and can read twenty pages an hour, there is a relationship between how many hours 
you read and how many pages you read. You may even know that you could write the formula as either: 



n = 20-h 
n 
20 



n = number of pages; 



h = time measured in hours. OR. 



h 



To graph this relation, you could make a chart. By picking values for the number of hours, you can 
determine the number of pages read. By graphing these coordinates, you can visualize the relation. 

Table 4.1: 



Hours 



Pages 



1 

1.5 
2 
3.5 

5 



20 
30 
40 
70 
100 



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122 




1 2 3 

Number of hours, h 

This relation appears to form a straight line. Therefore, the relationship between the total number of read 
pages and the number of hours can be called linear. The study of linear relationships is the focus of this 
chapter. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: The Coordinate Plane (6:50) 




Figure 4.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/749 



In questions 1-6, identify the coordinate of the given letter. 



1. D 

2. A 

3. F 

4. E 

5. B 

6. C 



123 



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< 


































\ 






B 








d - 


















































C 


2- 

* _ 


















































1 










X 


6 -5 -4 -3 -2 -1 4 


12 3 4 5 6 












-2- 

o _ 
























D 
































t 


i 


















-**- 








E 


















-6- 




— « 


F 

h — I 











Graph the following ordered pairs on one Cartesian plane. Identify the quadrant in which each ordered 
pair is located. 



7. (4, 2) 

8. (-3, 5.5) 

9. (4, -4) 
10. (-2, -3) 

11. M) 

12. (-0.75, 1) 

13. (-21,-6) 

14. (1.60, 4.25) 



In 15 - 22, using the directions given in each problem, find and graph the coordinates on a Cartesian plane. 



15. Six left, four down 

16. One-half right, one-half up 

17. Three right, five down 

18. Nine left, seven up 

19. Four and one-half left, three up 

20. Eight right, two up 

21. One left, one down 

22. One right, three-quarter down 

23. Plot the vertices of triangle ABC : (0, 0), (4, -3), (6, 2). 

24. The following three points are three vertices of square ABCD. Plot them on a coordinate plane then 
determine what the coordinates of the fourth point, D, would be. Plot that fourth point and label 
it. A(-4,-4) 5(3,-4) C(3,3) 

25. Does the ordered pair (2, 0) lie in a quadrant? Explain your thinking. 

26. Why do you think (0, 0) is called the origin? 

27. Becky has a large bag of M&Ms that she knows she should share with Jaeyun. Jaeyun has a packet 
of Starburst candy. Becky tells Jaeyun that for every Starburst he gives her, she will give him three 
M&Ms in return. If x is the number of Starburst that Jaeyun gives Becky, and y is the number of 
M&Ms he gets in return, then complete each of the following. 

(a) Write an algebraic rule for y in terms of x. 

(b) Make a table of values for y with x values of 0, 1, 2, 3, 4, 5. 



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124 



(c) Plot the function linking x and y on the following scale < x < 10,0 < y < 10. 

28. Consider the rule: y = ^x + 8. Make a table. Then graph the relation. 

29. Ian has the following collection of data. Graph the ordered pairs and make a conclusion from the 
graph. 

Table 4.2: 

Year % of Men Employed in the United States 

1973 75.5 

1980 72.0 

1986 71.0 

1992 69.8 

1997 71.3 

2002 69.7 

2005 69.6 

2007 69.8 

2009 64.5 

Mixed Review 

30. Find the sum: § + ± - §. 

31. Solve for m : 0.05m + 0.025(6000 - m) = 512. 

32. Solve the proportion for u : ^ = ^. 

33. What does the Additive Identity Property allow you to do when solving an equation? 

34. Shari has 28 apples. Jordan takes \ of the apples. Shari then gives away 3 apples. How many apples 
does Shari have? 

35. The perimeter of a triangle is given by the formula Perimeter = a + b + c, where a,b, and c are the 
lengths of the sides of a triangle. The perimeter of AABC is 34 inches. One side of the triangle is 12 
inches. A second side is 7 inches. How long is the remaining side of the triangle? 

36. Evaluate — — ^ — ~> f or x = 2 and y = -2. 

4.2 Graphs of Linear Equations 

In Chapter 3, you learned how to solve equations in one variable. The answer was of the form variable = 
some number. In this lesson, you will learn how to solve equations with two variables. Below are several 
examples of two- variable equations: 

p = 20(h) 
m = 8.15(h) 

y = 4x + 7 

You have seen each of these equations in a previous lesson. Their solutions are not one value because there 
are two variables . The solutions to these equations are pairs of numbers. These pairs of numbers can be 
graphed in a Cartesian plane. 

The solutions to an equation in two variables are sets of ordered pairs. 

The solutions to a linear equation are the coordinates on the graphed line. 

125 www.ckl2.org 



By making a table, you are finding the solutions to the equation with two variables. 

Example: A taxi fare costs more the further you travel Taxis usually charge a fee on top of the per-mile 
charge. In this case, the taxi charges $3 as a set fee and $0.80 per mile traveled. Find all the possible 
solutions to this equation. 

Solution: Here is the equation linking the cost in dollars (y) to hire a taxi and the distance traveled in 
miles (x): y = 0.8x + 3. 

This is an equation in two variables. By creating a table, we can graph these ordered pairs to find the 
solutions. 

Table 4.3: 



x (miles) 



y (cost $) 





10 

20 

30 

40 



3 

11 

19 

27 

35 









35 














2 


1 J f 




1 


^r 












1 


\^r 














Zjr 









The solutions to the taxi problem are located on the green line graphed above. To find any cab ride cost, 
you just need to find the y-ordinate of the desired x- abscissa. 

Multimedia Link: To see more simple examples of graphing linear equations by hand, view the video 

Khan Academy graphing lines (9:49) . 

The narrator of the video models graphing linear equations by using a table of values to plot points and 
then connecting those points with a line. This process reinforces the procedure of graphing lines by hand. 



Graphs of Horizontal and Vertical Lines 

Not all graphs are slanted or oblique. Some are horizontal or vertical. Read through the next situation 
to see why. 

Example: "Mad-cabs" have an unusual offer going on. They are charging $7.50 for a taxi ride of any 
length within the city limits. Graph the function that relates the cost of hiring the taxi (y) to the length of 



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126 




Figure 4.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/90 

the journey in miles (x) . 

Solution: No matter the mileage, your cab fare will be $7.50. To see this visually, create a graph. You can 
also create a table to visualize the situation. 



-10 
- a 






















_ a 






















- o 






















_ 7 






















- R 






















- D 

- ^ 






















- A 






















- 4 
-ft 






















* 9 






















- 1 










































X 



1 



8 9 10 



Table 4.4: 



# of miles (x) 



Cost (y) 





10 

15 

25 

60 



7.50 
7.50 
7.50 
7.50 
7.50 



Because the mileage can be anything, the equation should relate only to the restricted value, in this case, 
y. The equation that represents this situation is: 

y = 7.50 

Whenever there is an equation of the form y — constant, the graph is a horizontal line that intercepts the 
y-axis at the value of the constant. 

Similarly, if there is an equation of the form x = constant, the graph is a vertical line that intercepts the 
x-axis at the value of the constant. Notice that this is a relation but not a function because each x value 
(there's only one in this case) corresponds to many (actually an infinite number) y values. 

Example 1: Plot the following graphs. 

(a) y = 4 

(b) y = -4 



127 



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(b) y = -4 is a horizontal line that crosses the y-axis at -4. 

(c) x = 4 is a vertical line that crosses the x-axis at 4. 

(d) x = -4 is a vertical line that crosses the x-axis at -4. 













3 

6- 

5- 

A 


k 






















' 














^) 










-s _ 






















9_ 
















(d) 








A . 






(c) 








1 










1 


1 1 










X 


1 t 

6 -5 - 


L -3 -2 -1 A 


I 1 

1 : 


> 3 i 


i 5 6 












-2- 

-3- 

A 


'. 




\ 
























n 
















-5- 
-fi- 

























Analyzing Linear Graphs 



Analyzing linear graphs is a part of life - whether you are trying to decide to buy stock, figure out if your 
blog readership is increasing, or predict the temperature from a weather report. Although linear graphs 
can be quite complex, such as a six-month stock graph, many are very basic to analyze. 

The graph below shows the solutions to the price before tax and the price after tax at a particular store. 
Determine the price after tax of a $6.00 item. 

By finding the appropriate x-abscissa ($6.00), you can find the solution, the y-ordinate (approximately 
$6.80). Therefore, the price after tax of a $6.00 item is approximately $6.80. 



n 


- in 


















" tu 


















-8 
- 7 
































CO 


-6 
-5 

. A 












(c) 




c 
o 
































- 3 
-2 

- \y 

r 





























































X 



Price before tax {$) 

The following graph shows the linear relationship between Celsius and Fahrenheit temperatures. Using the 
graph, convert 70°F to Celsius. 



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128 



y 


-40 
- ^^ 
















y 






JO 














/ 


/ 




t/> 












y 


/ 










- £.3 






/ 










o 
o 


-20 






















0> 


no 
























I— 


- 1U 


























D 






















X 


Q_ 

E 


1 

--5 

--10 

-/& 


2C \A0 40 50 60 70 80 90 100 
/ Temperature in Fahrenheit 





































By finding the temperature of 70°F and locating its appropriate Celsius value, you can determine that 
70°F « 22°C. 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Graphs of Linear Equations (13:09) 



Video 



Figure 4.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/750 



1. What are the solutions to an equation in two variables? How is this different from an equation in 
one variable? 

2. What is the equation for the x-axisl 

3. What is the equation for the y—axisl 

4. Using the tax graph from the lesson, determine the net cost of an item costing $8.00 including tax. 

5. Using the temperature graph from the lesson, determine the following: 

(a) The Fahrenheit temperature of 0°C 

(b) The Fahrenheit temperature of 30°C 

(c) The Celsius temperature of 0°F 

(d) The Celsius equivalent to water boiling (212 F) 

6. Graph the following equations on separate Cartesian planes. 

(a) y = -2 

(b) 7 = x 



129 



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(c) 4.5 = y 

(d) x = 8 

The graph below shows a conversion chart for converting between the weight in kilograms to weight 
in pounds. Use it to convert the following measurements. 





-20 
























-18 
























" it) 
























- 14 
























--1Q 






















o 


IZ 






















D_ 


- 1y 

- Q 
























O 
- K 
























^J 
























- A 
























r\ > 
























s 
























/ i i i i i i i 


X 

1 1 w 


0123456789 10" 












Kile 


gran 


IS 











7. 4 kilograms into weight in pounds 

8. 9 kilograms into weight in pounds 

9. 12 pounds into weight in kilograms 
10. 17 pounds into weight in kilograms 

Write the equations for the graphed lines pictured below. 



















yj 


\ 






























oH-k 




































E 
























r 






































U 
























A 














A 






































4 






































o 










































































X 


-S -6 -< 




-2 








i 


I 


i 


) 8 




*-» 










B 




_4. 






































-D" 


















C 


































■u 





















11. £ 

12. B 

13. C 

14. A 

15. D 

16. At the airport, you can change your money from dollars into Euros. The service costs $5, and for 
every additional dollar you get 0.7 Euros. Make a table for this information and plot the function 
on a graph. Use your graph to determine how many Euros you would get if you give the exchange 
office $50. 



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130 



17. Think of a number. Triple it, and then subtract seven from your answer. Make a table 
of values and plot the function that this sentence represents. 

Find the solutions to each equation by making a table and graphing the coordinates. 

18. y = 2x + 7 

19. y = 0.7x-4 

20. y = 6-1.25* 

Mixed Review 

21. Find the percent of change: An item costing $17 now costs $19.50. 

22. Give an example of an ordered pair located in Quadrant III. 

23. Jodi has h of a pie. Her little brother asks for half of her slice. How much pie does Jodi have? 

24. Solve for b : b + 16 = 3b - 2. 

25. What is 16% of 97? 

26. Cheyenne earned a 73% on an 80-question exam. How many questions did she answer correctly? 

27. List four math verbs. 

4.3 Graphs Using Intercepts 

As you may have seen in the previous lesson, graphing solutions to an equation of two variables can be 
time-consuming. Fortunately, there are several ways to make graphing solutions easier. This lesson will 
focus on graphing a line by finding its intercepts. Lesson 4.5 will show you how to graph a line using its 
slope and y-intercept. 

In geometry, there is a postulate that states, "Two points determine a line." Therefore, to draw any line, 
all you need is two points. One way is to find its intercepts. 

An intercept is the point at which a graphed equation crosses an axis. 

The x-intercept is an ordered pair at which the line crosses the x-axis (the horizontal axis). Its ordered 
pair has the form (jc, 0). 

The y-intercept is an ordered pair at which the line crosses the y-axis (the vertical axis). Its ordered 
pair has the form (0,y) 

By finding the intercepts of an equation, you can quickly graph all the possible solutions to the equation. 

Finding Intercepts Using Substitution 

Remember that the Substitution Property allows the replacement of a variable with a numerical value or 
another expression. You can use this property to help find the intercepts of an equation. 

Example: Graph 2x + 3y = -6 using its intercepts. 

Solution: The x-intercept has an ordered pair (jc, 0). Therefore, the y-coordinate has a value of zero. By 
substituting zero for the variable of y, the equation becomes: 

2jc + 3(0) = -6 

Continue solving for x: 

131 www.ckl2.org 



2x + = -6 

2x = -6 

x = -3 

The x-intercept has an ordered pair of (-3, 0). 

Repeat the process to find the y-intercept. The ordered pair of the y-intercept is (0,y). Using substitution, 

2(0) + 3y = -6 

3y = -6 

y = -2 



The y-intercept has the ordered pair (0, -2). 

To graph the line formed by the solutions of the equation 2x + 3y 
connect them with a straight line. 



-6, graph the two intercepts and 



10 

















































































10 







Example: Graph 4x - 2y = 8 using its intercepts. 

Solution: Determine the x-intercept by substituting zero for the variable y. 

4jc-2(0) = 8 

4x = 8 

x = 2 



The ordered pair of the x-intercept is (2, 0). By repeating this process, you find the y-intercept has the 
ordered pair (0, -4). Graph these two ordered pairs and connect with a line. 



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132 



/ 

1 /I 

























































Finding Intercepts Using the Cover-Up Method 



By finding an intercept, you are substituting the value of zero in for one of the variables. 

To find the x-intercept, substitute zero for the y- value. 

To find the y-intercept, substitute zero for the x-value. 

A second method of finding the intercepts is called the Cover-Up Method. Using the Multiplication 
Property of Zero a(0) = 0, you can "cover-up" the other variable and solve for the intercept you wish to 
find. 

Example: Graph -7x - 3y = 21 using its intercepts. 

Solution: To solve for the y-intercept we set x = and cover up the x term: 



-3y = 21 



-3y = 21 
y = -7 



(0, -7) is the y - intercept. 



To solve for the x-intercept, cover up the y- variable and solve for x: 



-7x-tl= i 



-7x = 21 
x = -3 



(-3, 0) is the x - intercept. 



Now graph by first plotting the intercepts then drawing a line through these points. 

133 www.ckl2.or£ 



Example 1: Jose has $30 to spend on food for a class barbeque. Hot dogs cost $0.75 each (including the 
bun) and burgers cost $1.25 (including bun and salad). Plot a graph that shows all the combinations of hot 
dogs and burgers he could buy for the barbecue, spending exactly $30. 

Solution: Begin by translating this sentence into an algebraic equation. Let y = the number of hot dogs 
and x = the number of burgers. 



1.250) + 0.75(;y) = 30 



Find the intercepts of the graph. This example will use the Cover-Up Method. Feel free to use Substitution 
if you prefer. 



+ 0.75y=3C 



0.75;y = 30 
y = 40 



y - intercept^, 40) 



1.25X + I 1 = 30 



1.25* = 30 

x = 24 



x - intercept(2A, 0) 



By graphing Jose's situation, you can determine the combinations of hot dogs and burgers he can purchase 
for exactly $30.00. 



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134 

















+ 















Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Graphing Using Intercepts (12:18) 




Figure 4.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/751 



1. Define intercept 

2. What is the ordered pair for an x-intercept? 

3. Explain the process of the Cover-Up Method. 

Find the intercepts for the following equations using substitution. 

4. y = 3x-6 

5. y = -2;t + 4 

6. v= 14* -21 

7. y = 7 - 3x 

Find the intercepts of the following equations using the Cover-Up Method. 

8. 5x-6y= 15 



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9. 3jt-4y = -5 

10. 2x + 7y = -11 

11. 5x+10y = 25 

12. Do you prefer the Substitution Method or the Cover-Up Method? Why? 

In 13 - 24, use any method to find the intercepts and then graph the equation. 

13. y = 2x + 3 

14. 6(jc-1) = 2(y + 3) 

15. x -y = 5 

16. x + y = 8 

17. 4x + 9y = 

18. ±x + 4y = 12 

19. x-2y = 4 

20. 7x-5y= 10 

21. 4jt-y = -3 

22. x-y = 

23. 5x + y = 5 

24. 7x - 2y = -6 

25. Which intercept does a vertical line have? 

26. Does the equation y = 5 have both an x-intercept and a y-intercept? Explain your answer. 

27. Write an equation having only an x-intercept at (-4, 0). 

28. How many equations can be made with only one intercept at (0, 0)? Hint: Draw a picture to help 
you. 

29. What needs to be done to the following equation before you can use either method to find its 
intercepts? 3(jc + 2) = 2(y + 3) 

30. At the local grocery store, strawberries cost $3.00 per pound and bananas cost $1.00 per pound. If 

1 have $10 to spend between strawberries and bananas, draw a graph to show what combinations of 
each I can buy and spend exactly $10. 

31. A movie theater charges $7.50 for adult tickets and $4.50 for children. If the $900 theater takes in 
ticket sales for a particular screening, draw a graph that depicts the possibilities for the number of 
adult tickets and the number of child tickets sold. 

32. In football, touchdowns are worth 6 points, field goals are worth 3 points, and safeties are worth 

2 points. Suppose there were no safeties and the team scored 36 points. Graph the situation to 
determine the combinations of field goals and touchdowns the team could have had. 

Mixed Review 

Determine whether each ordered pair is a solution to the equation. 

33. 5x + 2y = 23; (7, -6) and (3, 4) 

34. 3a -2b = 6; (0,3) and(\^). 

35. Graph the solutions to the equation x = -5. 

36. Solve: f£-16 = -±. 

37. Is the following relation a function? {(-1, 1), (0, 0), (1, 1), (2, 3), (0, 6)} 

38. Using the number categories in Lesson 2.1, what is the best way to describe the domain of the 
following situation: The number of donuts purchased at a coffee shop on a particular day? 

39. Find the percent of change: Old price = $1,299; new price = $1,145. 

www.ckl2.org 136 



4.4 Slope and Rate of Change 

The pitch of a roof, the slant of a ladder against a wall, the incline of a road, and even your treadmill 
incline are all examples of slope. 

The slope of a line measures its steepness (either negative or positive). 

For example, if you have ever driven through a mountain range, you may have seen a sign stating, "10% 
incline." The percent tells you how steep the incline is. You have probably seen this on a treadmill too. 
The incline on a treadmill measures how steep you are walking uphill. Below is a more formal definition 
of slope. 

The slope of a line is the vertical change divided by the horizontal change. 

In the figure below, a car is beginning to climb up a hill. The height of the hill is 3 meters and the length 

3 

4* 



of the hill is 4 meters. Using the definition above, the slope of this hill can be written as | Meters ~~ ~ 



Because 4 = 75%, we can say this hill has a 75% positive slope. 




Similarly, if the car begins to descend down a hill, you can still determine the slope. 




Slope = 



vertical change 
horizontal change 



The slope in this instance is negative because the car is traveling downhill. 

Another way to think of slope is: slope = j^. 

When graphing an equation, slope is a very powerful tool. It provides the directions on how to get from 
one ordered pair to another. To determine slope, it is helpful to draw a slope-triangle. 

Using the following graph, choose two ordered pairs that have integer values such as (-3, 0) and (0, -2). 
Now draw in the slope triangle by connecting these two points as shown. 



137 



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I 



The vertical leg of the triangle represents the rise of the line and the horizontal leg of the triangle represents 
the run of the line. A third way to represent slope is: 

rise 

slope = 

run 

Starting at the left-most coordinate, count the number of vertical units and horizontal units it took to get 
to the right-most coordinate. 

__ rise _ ~ 2 _ 2 
run +3 3 

Example 1: Find the slope of the line graphed below. 

Solution: Begin by finding two pairs of ordered pairs with integer values: (1, 1) and (0, -2). 



5 






















































J 




























































































+ 






/ 










•!) 








/ 











Draw in the slope triangle. 

Count the number of vertical units to get from the left ordered pair to the right. 

Count the number of horizontal units to get from the left ordered pair to the right. 



rise +3 3 
S lope = = — = - 

run +1 1 



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138 



A more algebraic way to determine a slope is by using a formula. The formula for slope is: 

The slope between any two points (xi,yi) and (^2,^2) i s: slope = ^zj~- 

(jci,yi) represents one of the two ordered pairs and (JC2, J2) represents the other. The following example 
helps show this formula. 

Example 2: Using the slope formula, determine the slope of the equation graphed in Example 1. 

Solution: Use the integer ordered pairs used to form the slope triangle: (1, 1) and (0, -2). Since (1, 1) is 
written first, it can be called (x\,yi). That means (0,-2) = (x2,y2) 

Use the formula: slope = ^^ = =j^p = 5f = f 

As you can see, the slope is the same regardless of the method you use. If the ordered pairs are fractional 
or spaced very far apart, it is easier to use the formula than to draw a slope triangle. 



Types of Slopes 

Slopes come in four different types: negative, zero, positive, and undefined. The first graph of this lesson 
had a negative slope. The second graph had a positive slope. Slopes with zero slopes are lines without any 
steepness, and undefined slopes cannot be computed. 

Any line with a slope of zero will be a horizontal line with equation y = some number. 

Any line with an undefined slope will be a vertical line with equation x = some number. 

We will use the next two graphs to illustrate the previous definitions. 















Vi 


i 








B 


















R- 





























































Am 




























































n 


















1 












£. 
















X 


1 

-i 


> 


-4 




I 









I 


* 


\ 


1 




w 













































■£■■ 






























A 




























































{-: 

















































To determine the slope of line A, you need to find two ordered pairs with integer values. 

Sample: (-4, 3) and (1, 3). Choose one ordered pair to represent (x\,y{) and the other to represent (jc2,J2)- 



Now apply the formula: slope 



n-n 



3-3 



0. 



JC2-JC1 l-(-4) 1+4 

To determine the slope of line 5, you need to find two ordered pairs on this line with integer values and 
apply the formula. 

Sample: (5, 1) and (5, -6) 

slope = = = — = Undefined 

X2 - x\ 5-5 

It is impossible to divide by zero, so the slope of line B cannot be determined and is called undefined. 

139 www.ckl2.org 



Finding Rate of Change 

When finding the slope of real-world situations, it is often referred to as rate of change. "Rate of change" 
means the same as "slope." If you are asked to find the rate of change, use the slope formula or make a 
slope triangle. 

Example 3: Andrea has a part-time job at the local grocery store. She saves for her vacation at a rate of 
$15 every week. Find her rate of change. 

Solution: Begin by finding two ordered pairs. You can make a chart or use the Substitution Property to 
find two coordinates. 

Sample: (2, 30) and (10, 150). Since (2, 30) is written first, it can be called (xi,yi). That means 

(10,150) = (x 2 ,y 2 )- 

Use the formula: slope = g^ = ±fjgr = ™ = f- 

Andrea's rate of change is $15/1 week. 

Multimedia Link: For more information regarding rates of change, visit NCTM's website for an in- 
teractive - http://standards.nctm.Org/document/eexamples/chap6/6.2/part2.htm - rate of change 
activity. 

Example 4: A candle has a starting length of 10 inches. Thirty minutes after lighting it, the length is 
7 inches. Determine the rate of change in the length of the candle as it burns. Determine how long the 
candle takes to completely burn to nothing. 

Solution: Begin by finding two ordered pairs. The candle begins at 10 inches in length. So at time "zero", 
the length is 10 inches. The ordered pair representing this is (0, 10). 30 minutes later, the candle is 7 
inches, so (30, 7). Since (0, 10) is written first, it can be called (xi,yi). That means (30,7) = (x2,y2). 

Use the formula: slope — }2 ~ n 



X2~X\ 



7-10 
30-0 



=3 

30 



J_ 
10' 



The candle has a rate of change is -1 inch/ 10 minutes. To find the length of time it will take for the candle 
to burn out, you can create a graph, use guess and check, or solve an equation. 





y j 


MO 
















































































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20 40 W 80 


k 


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1: 


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time (minutes) 

You can create a graph to help visualize the situation. By plotting the ordered pairs you were given and 
by drawing a straight line connecting them, you can estimate it will take 100 minutes for the candle to 
burn out. 

Example: Examine the following graph. It represents a journey made by a large delivery truck on a 
particular day. During the day, the truck made two deliveries, each one taking one hour. The driver also 
took a one-hour break for lunch. Identify what is happening at each stage of the journey (stages A through 



www.ckl2.org 



140 



E). 



140 
120 



9" 100 
h 



80 
60 
40 

20 




- 








m 














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m 


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0123456789 

time (hours) 

Truck's Distance from Home by Time 

Here is the driver's journey. 

A. The truck sets off and travels 80 miles in 2 hours. 

B. The truck covers no distance for 1 hour. 

C. The truck covers (120 - 80) = 40 miles in 1 hour. 

D. The truck covers no distance for 2 hours. 

E. The truck covers 120 miles in 2 hours. 

Solution: To identify what is happening at each leg of the driver's journey you are being asked to find 
each rate of change. 

The rate of change for line segment A can be found using either the formula or the slope triangle. Using 
the slope triangle, vertical change = 80 and the horizontal change = 2. 

slope = r -m = §0*2*1 = 40 miles/1 hour. 

r run 2 hours ' 

Segments B and D are horizontal lines and each has a slope of zero. 

The rate of change for line segment C using the slope formula: Rate of change = ^ = (4-3) hours** ~ 
40 miles per hour. 

The rate of change for line segment E using the slope formula: Rate of change = f^ = (s-6) hours' = 
~2 hours eS = ~®® m il es P er hour. The truck is traveling at negative 60 mph. A better way to say this is 
that the truck is returning home at a rate of 60 mph. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Slope and Rate of Change (13:42) 

1. Define slope. 

2. How is slope related to rate of change? In what ways is it different? 

3. Describe the two methods used to find slope. Which one do you prefer and why? 

4. What is the slope of all vertical lines? Why is this true? 

5. What is the slope of all horizontal lines? Why is this true? 



141 



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Figure 4.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/752 



Using the graphed coordinates, find the slope of each line. 















y 1 


i 






a. 






















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www.ckl2.org 



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In 9 - 21, find the slope between the two given points. 



9. 
10. 
11. 

12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 



-5, 7) and (0, 0) 
-3, -5) and (3, 11) 
3, -5) and (-2, 9) 
-5, 7) and (-5, 11) 
9, 9) and (-9, -9) 
3, 5) and (-2, 7) 
\, \ ) and (-2, 6) 
-2, 3) and (4, 8) 
-17, 11) and (4, 11) 
31, 2) and (31, -19) 
0, -3) and (3, -1) 
2, 7) and (7, 2) 
0, 0) and (§, \) 
Determine the slope of y 



= 16. 

23. Determine the slope of x = -99. 

24. The graph below is a distance-time graph for Mark's 3.5-mile cycle ride to school. During this 
particular ride, he rode on cycle paths but the terrain was hilly. His speed varied depending upon 
the steepness of the hills. He stopped once at a traffic light and at one point he stopped to mend a 
tire puncture. Identify each section of the graph accordingly. 



3.5- 



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0- 


















— i 



2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 
time (minutes) 



143 



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25. Four hours after she left home, Sheila had traveled 145 miles. Three hours later she had traveled 300 
miles. What was her rate of change? 

26. Jenna earns $60 every 2^ weeks. What is her rate of change? 

27. Geoffrey has a rate of change of 10 feet/1 second. Write a situation that could fit this slope. 

Mixed Review 

28. Find the intercepts of 3x - 5y = 10. 

29. Graph the line y = -6. 

30. Draw a line with a negative slope passing through the point (3, 1). 

31. Draw a graph to represent the number of quarter and dime combinations that equal $4.00. 

32. What is the domain and range of the following: {(-2, 2), (-1, 1), (0, 0), (1, 1), (2, 2)}? 

33. Solve for y : 16y - 72 = 36. 

34. Describe the process used to solve an equation such as: 3x + 1 = 2x - 35. 

35. Solve the proportion: | = ^j+i- 



Quick Quiz 



1. Find the intercepts of 3x + 6y = 25 and graph the equation. 

2. Find the slope between (8, 5) and (-5, 6). 

3. Graph f(x) =2x+l. 

4. Graph the ordered pair with the following directions: 4 units west and 6 units north of the origin. 

5. Using the graph below, list two "trends" about this data. A trend is something you can conclude 
about the given data. 



U.S. Public School Student Membership (in millions) 



43 



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1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 

SOURCE: Notional Center for Education Statistics, Common Core 
at Data (CCD) 



4.5 Graphs Using Slope-Intercept Form 

So far in this chapter, you have learned how to graph the solutions to an equation in two variables by- 
making a table and by using its intercepts. The last lesson introduced the formulas for slope. This lesson 
will combine intercepts and slope into a new formula. 



www.ckl2.org 



144 



You have seen different forms of this formula several times in this chapter. Below are several examples. 

2x + 5 = y 

y =T x+n 

d = 60(A) +45 

The proper name given to each of these equations is slope-intercept form because each equation tells 
the slope and the y-intercept of the line. 

The slope-intercept form of an equation is: y = (slope)x-\- (y— intercept). 

y = (m)x + /?, where m = slope and b = y-intercept 

This equation makes it quite easy to graph the solutions to an equation of two variables because it gives 
you two necessary values: 

1. The starting position of your graph (the y-intercept) 

2. The directions to find your second coordinate (the slope) 

Example 1: Determine the slope and they- intercept of the first two equations in the opener of this lesson. 

Solution: Using the definition of slope-intercept form; 2x + 5 = y has a slope of 2 and a y-intercept of 

(0,5) 

y = ^x + 11 has a slope of ^ and a y-intercept of (0, 11) 

Slope-intercept form applies to many equations, even those that do not look like the "standard" equation. 

Example: Determine the slope and y-intercept of7x = y. 

Solution: At first glance, this does not look like the "standard" equation. However, we can substitute 
values for the slope and y-intercept. 

7x + = y 

This means the slope is 7 and the y-intercept is 0. 

Example: Determine the slope and y-intercept of y = 5. 

Solution: Using what you learned in the last lesson, the slope of every line of the form y = some number 
is zero because it is a horizontal line. Rewriting our original equation to fit slope-intercept form yields: 

y= (0)jt+5 

Therefore, the slope is zero and the y-intercept is (0, 5). 

You can also use a graph to determine the slope and y-intercept of a line. 

Example: Determine the slope and y-intercept of the lines graphed below. 

Solution: Beginning with line a, you can easily see the graph crosses the y-axis (the y-intercept) at (0, 
5). From this point, find a second coordinate on the line crossing at a lattice point. 

145 www.ckl2.org 











i 


.. y 1 


* b. 


< 




















1 


y 


















A- 


J 




/ 






























































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d 






























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line a; The y-intercept is (0, 5). The line also passes through (2, 3). 

i Ay -2 

slope m = — = — = -1 

Lme /?: The y-intercept is (0, 2). The line also passes through (1, 5). 

slope m = — = - = 3 

Ajc 1 

The remaining lines will be left for you in the Practice Set. 

Graphing an Equation Using Slope-Intercept Form 

Once we know the slope and the y-intercept of an equation, it is quite easy to graph the solutions. 

Example: Graph the solutions to the equation y = 2x + 5. 

Solution: The equation is in slope-intercept form. To graph the solutions to this equation, you should 
start at the y-intercept. Then, using the slope, find a second coordinate. Finally, draw a line through the 
ordered pairs. 



y A 


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1R -7 


:: 18 t\ 




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.. 14 J2 f / \ 


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A: 4 




■ '2 


trr 1 1 [ 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 ► 

01 2 4 6 8 10 12 14 16 18 20 



Example 2: Graph the equation y = -3x + 5 



www.ckl2.org 



146 



Solution: Using the definition of slope-intercept form, this equation has a y-intercept of (0, 5) and a 
slope of ^p. 




Slopes of Parallel Lines 

Parallel lines will never intersect, or cross. The only way for two lines never to cross is if the method 
of finding additional coordinates is the same. 

Therefore, it's true that parallel lines have the same slope. 

You will use this concept in Chapter 5 as well as in geometry. 

Example 3: Determine the slope of any line parallel to y = -3x + 5 

Solution: Because parallel lines have the same slope, the slope of any line parallel to y = -3x + 5 must 
also be -3. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Graphs Using Slope-Intercept Form (11:11) 




Figure 4.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/753 



In 1 - 7, identify the slope and y-intercept for the equation. 

147 



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1. y = 2x + 5 

2. y = -0.2x + 7 

3. y = x 

4. y = 3.75 

5. §je-9 = y 

6. y = -0.01x+10,000 
3--, 



7. 7+-x 



In 8 - 14, identify the slope of the following lines. 
A B 




8. F 

9. C 

10. A 

11. G 

12. B 

13. D 

14. F 



In 15 - 20, identify the slope and y— intercept for the following functions. 













y 4 


i 


B 










A 


N 








i> 




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s. 




4 




















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N 




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1 


I 


r>^4 f 


^ 












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n 
























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^ 








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f 










































F 










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-s- 















15. D 

16. A 

17. F 

18. B 

19. F 

20. C 

21. Determine the slope and y— intercept of -5x + 12 = 20. 

Plot the following functions on a graph. 
www.ckl2.org 148 



22. y = 2x+5 

23. y = -0.2x + 7 

24. y = -x 

25. j = 3.75 

26. fx-4 = y 

27. y = -4x+13 

28. -2 + §x = y 



29. y 



+ 2x 



In 30 - 37, state the slope of the line parallel to the line given. 

30. y = 2x + 5 

31. y = -0.2x + 7 

32. y = -x 

33. y = 3.75 

34. y = -i x -n 

35. y — -5x + 5 

36. y = -3x+ll 

37. y = 3x + 3.5 

Mixed Review 

38. Graph x — 4 on the Cartesian plane. 

39. Solve for g:\8-U\ + 4g = 99. 

40. What is the Order of Operations? When is the Order of Operations used? 

41. Give an example of a negative irrational number. 

42. Give an example of a positive rational number. 

43. True or false: An integer will always be considered a rational number. 

4.6 Direct Variation 

At the local farmer's market, you saw someone purchase 5 pounds of strawberries and pay $12.50. You 
want to buy strawberries too, but you want only 2 pounds. How much would you expect to pay? 




This situation is an example of a direct variation. You would expect that the strawberries are priced on 
a "per pound" basis, and that if you buy two-fifths of the amount of strawberries, you would pay two-fifths 
of $12.50 for your strawberries, or $5.00. Similarly, if you bought 10 pounds of strawberries (twice the 



149 



www.ckl2.org 



amount), you would pay $25.00 (twice $12.50), and if you did not buy any strawberries you would pay 
nothing. 

Direct Variation can be expressed as the equation y = (k)x, where k is called the constant of variation. 

Direct variation occurs when: 



The fraction 



rise ^ change in y 
change in x 



or 



is always the same, and 



• The ordered pair (0, 0) is a solution to the situation. 

Example: If y varies directly with x according to the relationship y = k • x, and y = 7.5 when x = 2.5 ; 
determine the constant of proportionality, k. 

Solution: We can solve for the constant of proportionality using substitution. 

Substitute x = 2.5 and y = 7.5 into the equation y = k • x. 



7.5 = £(2.5) 
2.5 



Divide both sides by 2.5. 



The constant of variation (or the constant of proportionality) is 3. 

You can use this information to graph this direct variation situation. Remember that all direct variation 
situations cross the origin. You can plot the ordered pair (0, 0) and use the constant of variation as your 
slope. 





k 












10 














O - 














8 




















C - 














6 




























4" 














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Example: Explain why each of the following equations are not examples of direct variation. 

2 

y = - 

x 
y = 5x - 1 

2x + y = 6 

Solution: In equation 1, the variable is in the denominator of the fraction, violating the definition. 
In equation 2, there is a y-intercept of -1, violating the definition. 
In equation 3, there is also a y-intercept, violating the definition. 



www.ckl2.org 



150 



Translating a Sentence into a Direct Variation Equation 

Direct variation equations use the same phrase to give the reader a clue. The phrase is either "directly 
proportional" or "varies directly." 

Example: The area of a square varies directly as the square of its side. 

Solution: The first variable you encounter is "area." Think of this as your y. Think the phrase "varies 
directly" means = (k)x. The second variable is "square of its side." Call this letter s. 

Now translate into an equation: y = (k)xs 2 . 

You've written your first direct variation equation. 

Example 2: The distance you travel is directly proportional to the time you have been traveling. Write 
this situation as a direct variation equation. 

Solution: The first variable is distance; call it d. The second variable is time you have been traveling, call 
it t. Apply the direct variation definition: 

d = (k) x t 

Solving Real- World Situations Using Direct Variation 

Direct variation has numerous real- world examples. You have already seen three examples: the area of a 
square is directly proportional to its side length; the distance you travel varies directly as the time you 
have been driving; and the total cost is directly proportional to the number of pounds of strawberries you 
purchase. 

Newton's Second Law 

In 1687, Sir Isaac Newton published the famous Principea Mathematica. It contained his Second Law of 
Motion. This law is often written as: F = m • a, where F = the amount of force applied to an object with 
mass (m) and a = acceleration. 

Acceleration is given in the units meters/ second 2 and force is given in units of Newtons. 

Example: If a 175 Newton force causes a heavily loaded shopping cart to accelerate down the aisle with 
an acceleration of 2.5 m/s 2 , calculate: 

(i) The mass of the shopping cart. 

(ii) The force needed to accelerate the same cart at 6 m/s 2 . 

Solution: (i) This question is basically asking us to solve for the constant of proportionality. Let us 
compare the two formulas. 

y = k - x The direct variation equation 

F = m - a Newton's Second law 

We see that the two equations have the same form. The variable y is equal to force and x is equal to 
acceleration. 



Now solve for m, the constant of variation. 



175 = m- 2.5 



175 m-2.5 



2.5 2.5 

m = 70 



151 www.ckl2.org 



(ii) Now you know the constant of variation is 70. In this formula, 70 represents the mass. To find the 
force needed to move the cart at an accelerated rate of 6 meters/ second, substitute 6 for a and evaluate 
the equation. 

When a = 6, F = 70 • 6 = 420. 

The force needed to accelerate the cart is 420 Newtons. 

Solving Direct Variation Using Proportions 

You can use the Cross Products Theorem of proportions to solve direct variation situations. Because the 
fraction rj ^- is constant in a direct variation situation, you can create a proportion. 

Ohm's Law states that the voltage (V) is equal to the electrical current (/) in amps times the resistance 
(R) in ohms. Translating this to an equation, V = I • R. 

Suppose an electronics device passed a current of 1.3 amps at a voltage of 2.6 volts. What was the current 
when the voltage was increased to 12 volts? 

Ohm's Law matches with the definition of direct variation, so you can write a proportion. 2 -^ volts = 12 volts . 

' J xr r l.j amps I amps 

Using the Cross Products Theorem, solve for /. 1 = 6. Therefore, when the voltage was increased to 12 
volts, the electronics device passed a current of 6 amps. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Direct Variation Models (11:11) 




Figure 4.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/754 



1. Describe direct variation. 

2. What is the formula for direct variation? What does k represent? 

3. What two methods can be used to solve a direct variation situation? 

4. True or false7 Every linear equation is a direct variation situation. 



Translate the following direct variation situations into equations. Choose appropriate letters to represent 
the varying quantities. 

5. The amount of money you earn is directly proportional to the number of hours you work. 

6. The weight of an object on the Moon varies directly with its weight on Earth. 



www.ckl2.org 



152 



7. The volume of a gas is directly proportional to its temperature in Kelvin. 

8. The number of people served varies directly with the amount of ground meat used to make burgers. 

9. The amount of a purchase varies directly with the number of pounds of peaches. 

Explain why each equation is not an example of direct variation. 

11. y = 9 

12. x = -3.5 

13. y= ±x + 7 

14. 4x + Sy = 1 

Graph the following direct variation equations. 



15. 


y = 


3 X 


16. 


y = 


6 A 


17. 


y = 



18. y = 1.75a: 

19. Is y = 6x - 2 an example of direct variation? Explain your answer. 

In 20 - 24, determine the constant of variation in each exercise. 

20. y varies directly as x; when x = 4,y = 48 

21. d varies directly as t; when t = 7, d = 329 

22. / varies directly as h; when I = 112 ; h = -16 

23. m is directly proportional to h; when m = 461.50, h = 89.6 

24. z is directly proportional to r; when r = 412, z = 51.5 

25. Determine the equation of the strawberry purchase in the opener of this lesson. 

26. Dasan's mom takes him to the video arcade for his birthday. In the first 10 minutes, he spends $3.50 
playing games. If his allowance for the day is $20.00, how long can he keep playing games before his 
money is gone? 

27. The current standard for low-flow showerheads is 2.5 gallons per minute. Calculate how long it would 
take to fill a 30-gallon bathtub using such a showerhead to supply the water. 

28. An electrical device passes a force of 288 volts at 32 amps. Using Ohm's Law, determine: 

(a) The constant of proportionality 

(b) The force needed to pass 65 amps 

29. The diameter of a circle is directly proportional to its radius. If a circle with a 2-inch diameter has 
a circumference of approximately 6.28 inches, what is the circumference of a 15-inch circle? 

30. Amin is using a hose to fill his new swimming pool for the first time. He starts the hose at 10:00 
P.M. and leaves it running all night. At 6:00 A.M. he measures the depth and calculates that the 
pool is four-sevenths full. At what time will his new pool be full? 

31. Land in Wisconsin is for sale to property investors. A 232-acre lot is listed for sale for $200,500. 
Assuming the same price per acre, how much would a 60-acre lot sell for? 

32. The force (F) needed to stretch a spring by a distance x is given by the equation F = k- x, where k 
is the spring constant (measured in Newtons per centimeter, N/cm). If a 12-Newton force stretches 
a certain spring by 10 cm, calculate: 

(a) The spring constant, k 

(b) The force needed to stretch the spring by 7 cm 

153 www.ckl2.org 



(c) The distance the spring would stretch with a 23-Newton force 
33. Determine the equations of graphs a - d below. 







y 1 


i 




























p 






i 






















































A 




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1 
























\ 0. 




a 
















d" 
























— * 








/ 




















X 


V"^-^L_ 6 I 


j 


1 











/ 


' b 




































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£ 


























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Mixed Review 



34. Graph 3x + 4y = 48 using its intercepts. 

35. Graph y = |x-4. 

36. Solve for u : 4(m + 3) = 3(3w - 7). 

37. Are these lines parallel? y — \x-7 and 2y 

38. In which quadrant is (-99, 100)? 

39. Find the slope between (2, 0) and (3, 7). 

40. Evaluate if a = -3 and b = 4: ±±||. 



JK + 2 



4.7 Linear Function Graphs 



So far, the term function has been used to describe many of the equations we have been graphing. The 
concept of a function is extremely important in mathematics. Not all equations are functions. To be a 
function, for each value of x there is one and only one value for y. 

Definition: A function is a relationship between two variables such that the input value has ONLY one 
unique output value. 

Recall from Lesson 1.5 that a function rule replaces the variable y with its function name, usually f(x). 
Remember that these parentheses do not mean multiplication. They separate the function name from the 
independent variable, x. 

input 

i 

f(x) = y <— output 

function 
box 

f(x) is read "the function / of jc" or simply "/ of x." 

If the function looks like this: h(x) = 3x - 1, it would be read h of x equals 3 times x minus 1. 



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154 



Using Function Notation 



Function notation allows you to easily see the input value for the independent variable inside the paren- 
theses. 

Example: Consider the function f(x) = -\x 2 . 

Evaluate /(4). 

Solution: The value inside the parentheses is the value of the variable x. Use the Substitution Property 
to evaluate the function for x = 4. 



/(4) = 4(4 



/(4) 
/(4) 



16 



To use function notation, the equation must be written in terms of x. This means that the y-variable must 
be isolated on one side of the equal sign. 

Example: Rewrite 9x + 3y = 6 using function notation. 

Solution: The goal is to rearrange this equation so the equation looks like y =. Then replace y = with 



9x + 3y = 6 

3 y = 6 - 9x 

6-9jc 

y= — 

f(x) = 2 - 3x 



= 2-3x 



Subtract 9x from both sides. 
Divide by 3. 



Functions as Machines 

You can think of a function as a machine. You start with an input (some value), the machine performs 
the operations (it does the work), and your output is the answer. For example, f(x) = 3x + 2 takes some 
number, jc, multiplies it by 3 and adds 2. As a machine, it would look like this: 



input 



x3 



+2 



output 



When you use the function machine to evaluate /(2), the solution is f{2) = 8. 
Example 1: A function is defined as f(x) = 6x - 36. Determine the following: 

a) /(2) 

b) f(p) 
Solution: 

a) Substitute x = 2 into the function f(x) : /(2) = 6 • 2 - 36 = 12 - 36 = -24. 

b) Substitute x = p into the function f{x) : f(p) = 6p - 36. 



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Graphing Linear Functions 



You can see that the notation f(x) = and y = are interchangeable. This means you can substitute the 
notation y = for f{x) = and use all the concepts you have learned in this chapter. 



Graph f{x) = -x + 1 
o 

Replace f(x) = with y - 



This equation is in slope-intercept form. You can now graph the function by graphing the y-intercept and 
then using the slope as a set of directions to find your second coordinate. 

Example: Graph f{x) = ^. 

Solution: The first step is to rewrite the single fraction as two separate fractions. 



_, N 3x + 5 3 5 

f\ x ) = — : — = ~* x + 7 
w 4 4 4 



This equation is in slope-intercept form. The y-intercept is at the ordered pair (0, |) and the slope is 
j^ = | . Beginning at the y-intercept and using the slope to find a second coordinate, you get the graph: 




1 2 3 4 5 6 7 8 



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156 



Analyzing Graphs of Real- World Linear Functions 



Taxes Paid 
(thousands of 
dollars) 




The previous graph, written by T. Barron and S. Katsberg from the University of Georgia http://jwilson. 
coe.uga.edu/emt668/EMAT6680.Folders/Barron/unit/Lesson°/o204/4.html, shows the relationship be- 
tween the salary (in thousands of dollars) and the taxes paid (in thousands of dollars) in red. The blue 
function represents a direct variation situation in which the constant of variation (or the slope) is 0.30, or 
a 30% tax rate. This direct variation represents a flat tax of 30%. 

The red line has three slopes. The first line from $0 to $15,000 has a slope of 0.20, or 20%. The second 
portion of the line from $15,000 to $45,000 has a slope of 0.25, or 25% tax rate. The slope of the line 
greater than $45,000 of salary is 0.35, or 35%. 

Suppose you wanted to compare the amount of taxes you would pay if your salary was $60,000. If the blue 
line was blue(s) and the red line was red(s), then you would evaluate each function for s = 60,000. 

Using the graph, blue(60) = 18 and red(60) = 15. Therefore, you would pay more taxes with the blue line 
tax rate than the red line tax rate. We will look at how to use graphs as a problem-solving strategy in the 
next lesson. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Linear Function Graphs (11:49) 



1. How is f{x) read? 

2. What does function notation allow you to do? Why is this helpful? 

3. Define function. How can you tell if a graph is a function? 



In 4 - 7, tell whether the graph is a function. Explain your reasoning. 

157 



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Figure 4.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/755 




6. 



7. 




x 




Rewrite each equation using function notation. 



8. y = 7x-21 
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158 



9. 6x + 8y = 36 

10. x = 9y + 3 

11. y = 6 

12. d = 65t + 100 

13. F= 1.8C + 32 

14. s = 0.10(m) + 25,000 

In 15 - 19, evaluate /(-3);/(7);/(0), and f(z). 

15. f{x) = -2x + 3 

16. f( x ) = 0.7jc + 3.2 

17. /(x) = 5M 

18. f(t) = ±t* + 4 

19. /(jc) = 3 - \x 

20. The roasting guide for a turkey suggests cooking for 100 minutes plus an additional 8 minutes per 
pound. 

(a) Write a function for the roasting time, given the turkey weight in pounds (x). 

(b) Determine the time needed to roast a 10-lb turkey. 

(c) Determine the time needed to roast a 27-lb turkey. 

(d) Determine the maximum size turkey you could roast in 4^ hours. 

21. F(C) = 1.8C + 32 is the function used to convert Celsius to Fahrenheit. Find F(100) and explain 
what it represents. 

22. A prepaid phone card comes with $20 worth of calls. Calls cost a flat rate of $0.16 per minute. Write 
the value of the card as a function of minutes per call. Use a function to determine the number of 
minutes of phone calls you can make with the card. 

23. You can burn 330 calories during one hour of bicycling. Write this situation using b(h) as the function 
notation. Evaluate b(0.75) and explain its meaning. 

24. Sadie has a bank account with a balance of $650.00. She plans to spend $55 per week. 

(a) Write this situation using function notation. 

(b) Evaluate her account after 10 weeks. What can you conclude? 

Mixed Review 

25. Simplify -120 (!)(§)• 

26. Find the sum: 7\ + 3§ + 5§ . 

27. Simplify -3(4m+ 11). 

28. Is the following situation an example of a function? Let x = salary and y = taxes paid. 

29. y varies directly as z, and y = 450 when z = 6. Find the constant of variation. 

30. Car A uses 15 gallons of gasoline to drive 2.5 hours. How much gas would this car use if it were 
driving 30 minutes? 

4.8 Problem- Solving Strategies: Read a Graph; 
Make a Graph 

Graphing is a very useful tool when analyzing a situation. This lesson will focus on using graphs to help 
solve linear situations that occur in real life. 

Remember the 4-Step Problem-Solving Plan: 

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1. Understand the problem and underline or highlight key information. 

2. Translate the problem and devise a method to solve the problem. 

3. Carry out the plan and solve the problem. 

4. Check and interpret your answer. Does it make sense? 

Example: A cell phone company is offering its costumers the following deal. You can buy a new cell 
phone for $60 and pay a monthly flat rate of $40 per month for unlimited calls. How much money will this 
deal cost you after 9 months? 

Solution: Begin by translating the sentence into an algebraic equation. 

cell phone = $60, calling plan = $40 per month 

Let m =the number of months and t = total cost. The equation becomes 

t{m) = 60 + 40m 

You could use guess and check or solve this equation. However, this lesson focuses on using a graph to 
problem-solve. This equation is in slope-intercept form. By graphing the line of this equation, you will 
find all the ordered pairs that are solutions to the cell phone problem. 



n 


- ^no 




Cost of Cell Phone by 
Number of Months 










O 

o 


" 3UU 
















/ 






















/ 










-Ann 














*4UU 






















-*wi 




















































_ inn 


























- Z\j\j 


























/ 






















































I I 






i i 


i i 


j 








L 


X 



1 2 3 4 5 6 7 8 9 10 11 12 
Number of months 

Finding the cost at month 9, you can see the cost is approximately $425.00. To check if this is approximately 
correct, substitute 9 in for the variable m. 

Phone = $60 
Calling plan = $40 x 9 = $360 
Total cost = $420. 



Our answer, $425.00 is approximately equal to the exact solution $420.00. 

Example: Christine took one hour to read 22 pages of "Harry Potter and the Order of the Phoenix." She 
has 100 pages left to read in order to finish the book. Assuming that she reads at a constant rate of pages 
per hour, how much time should she expect to spend reading in order to finish the book? 



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160 




Solution: We do not have enough information to write an equation. We do not know the slope or the 
y-intercept. However, we have two points we can graph. We know that if Christine had never picked up 
the book, she would have read zero pages. So it takes Christine hours to read pages. We also know it 
took Christine one hour to read 22 pages. The two coordinates we can graph are (0, 0) and (1, 22). 



Number of Pages Read by Time 



U 





- zu 


u 






















- 15 


n 




















Qj 














































S 


-*e 


B — 
























-50 
















































/ i i 


















X 




123456789 1(f 


















7 


ime 


In h 


DtirSj 





Using the graph and finding 100 pages, you can determine it will take Christine about 4.5 hours to read 
100 pages. 

You can also think of this as a direct variation situation and solve it by writing a proportion. 

22 pages 100 pages 



1 hour 



h hours 



By using the Cross Products Theorem, you can find out h « 4.55. It will take Christine about 4.55 hours 
to read 100 pages, which is very close to your original estimate of 4.5 hours. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Word Problem Solving 4 (10:05) 



1. Using the following graph, determine these values: 

161 



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Figure 4.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/756 



(a) The amount of earnings after 40 hours 

(b) How many hours it takes to earn $250.00 

(c) The slope of the line and what it represents 

(d) The y-intercept of the line and what it represents 



Aatifs Earnings by Hours Worked 




30 40 

Time (in hours) 

2. A stretched spring has a length of 12 inches when a weight of 2 lbs is attached to it. The same spring 
has a length of 18 inches when a weight of 5 lbs is attached to it. It is known from physics that 
within certain weight limits, the function that describes how much a spring stretches with different 
weights is a linear function. What is the length of the spring when no weights are attached? 




12in 




18ir 



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162 



3. A gym is offering a deal to new members. Customers can sign up by paying a registration fee of $200 
and a monthly fee of $39. How much will this membership cost a member by the end of one year? 

4. A candle is burning at a linear rate. The candle measures five inches two minutes after it was lit. It 
measures three inches eight minutes after it was lit. What was the original length of the candle? 

5. Tali is trying to find the thickness of a page of his telephone book. To do this, he takes a measurement 
and finds out that 550 pages measure 1.25 inches. What is the thickness of one page of the phone 
book? 

6. Bobby and Petra are running a lemonade stand and they charge 45 cents for each glass of lemonade. 
To break even, they must make $25. How many glasses of lemonade must they sell to break even? 

7. The tip for a $78.00 restaurant bill is $9.20. What is the tip for a $21.50 meal? 

8. Karen left her house and walked at a rate of 4 miles /hour for 30 minutes. She realized she was late 
for school and began to jog at a rate of 5.5 miles/ hour for 25 minutes. Using a graph, determine how 
far she is from her house at the end of 45 minutes. 



Mixed Review 



9. Simplify -4| - 21 - 11| + 16. 

10. Give an example of a direct variation equation and label its constant of variation. 

11. Identify the slope and y-intercept: |x = y - 4. 

12. Suppose A = (x,y) is located in quadrant I. Write a rule that would move A into quadrant III. 

13. Find the intercepts of 0.04.x + 0.06y = 18. 

14. Evaluate /(4) when f(x) = ^. 



4.9 Chapter 4 Review 

Define the following words: 



1. x- intercept 

2. y— intercept 

3. direct variation 

4. parallel lines 

5. rate of change 



In 6 - 11, identify the coordinates using the graph below. 

163 www.ckl2.org 



• E 

1 - • D 

4 " i " " 1 " i " ilk. 


1 B -1 

-1 

• F 


. 1 ; 

• c 

r 



6. D 

7. F 

8. A 

9. E 

10. B 

11. C 

In 12 - 16, graph the following ordered pairs on one Cartesian Plane. 

12. (1,-4) 

13. (-6, 1) 

14. (0, -5) 

15. (8, 0) 

16.(1,!) 
In 17 and 18, graph the function using the table. 



17. 



Table 4.5: 



-2 
-1 



7 
9 



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164 



Table 4.5: (continued) 



X 










y 



















11 








1 










13 








2 










15 








18. 




















d 





1 


2 


3 


4 


5 


6 




t 





75 


150 


225 


300 


375 


450 



In 19 - 24, graph the following lines on one set of axes. 

19. y = -% 

20. x = 4 

21. y = 5 

22. x = -3 

23. x = 

24. y = 

In 25 - 28, find the intercepts of each equation. 

25. y = 4x - 5 

26. 5x + 5y = 20 

27. x + ;y = 7 

28. 8y-16x = 48 

In 29 - 34, graph each equation using its intercepts. 

29. 3x + 7y = 21 

30. 2j - 5x = 10 

31. x-y = 4 

32. 16x + 8y = 16 

33. x + 9y = 18 

34. 7 + j= ijc 

In 35 - 44, find the slope between the sets of points. 



35. 
36. 
37. 
38. 
39. 
40. 
41. 
42. 
43. 
44. 



3, 20) and (19, 8) 

12, 5) and (12, 0) 
^-,5) and (|,3) 
8, 3) and (12, 3) 

14, 17) and (-14, -22) 
1, 4) and (18, 6) 
10, 6) and (10, -6) 
-3, 2) and (19, 5) 

13, 9) and (2, 9) 
10, -1) and (-10, 6) 



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In 45 - 50, determine the rate of change. 

45. Charlene reads 150 pages in 3 hours. 

46. Benoit cuts 65 onions in 1.5 hours. 

47. Brad drives 215 miles in 3.9 hours. 

48. Reece completes 65 jumping jacks in one minute. 

49. Harriet is charged $48.60 for 2,430 text messages. 

50. Samuel can eat 65 hotdogs in 22 minutes. 

In 51 - 55, identify the slope and the y-intercept of each equation. 



51. 


x + y — 3 


52. 


\x = 7 + y 


53. 


y=fx + 3 


54. 


x = 4 


55. 


y = \ 



In 56 - 60, graph each equation. 

56. y= jjx-1 

57. y = x 

58. y = -2jc + 2 

59. y = -§;c + 5 

60. y = -Jc + 4 

In 61 - 63, decide whether the given lines are parallel. 

61. 3x + 6y = 8 and y = 2x - 8 

62. y = x + 7 and y = -7 - x 

63. 2x + 4y = 16 and y = =^-x + 6 

In 64 - 70, evaluate the function for the indicated value. 

64. g(n) = -2|n-3|; Find g(7). 

65. h(a) = a 2 -4a; Find h(S). 

66. p(t) = 3f+l; Find^(^). 

67. g(x)=4|x|;Findg(-3). 

68. h(ri) = gii-4; Find A(24). 

69. /(jc) = *±5; Find/(20). 

70. r(c) = 0.06(c) + c; Find r(26.99). 

71. The distance traveled by a semi-truck varies directly with the number of hours it has been traveling. 
If the truck went 168 miles in 4 hours, how many miles will it go in 7 hours? 

72. The function for converting Fahrenheit to Celsius is given by C(F) = -y§-. What is the Celsius 
equivalent to 84° F? 

73. Sheldon started with 32 cookies and is baking more at a rate of 12 cookies/ '30 minutes. After how 
many hours will Sheldon have 176 cookies? 

74. Mixture A has a 12% concentration of acid. Mixture B has an 8% concentration of acid. How much 
of each mixture do you need to obtain a 60-ounce solution with 12 ounces of acid? 

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75. The amount of chlorine needed to treat a pool varies directly with its size. If a 5,000-gallon pool 
needs 5 units of chlorine, how much is needed for a 7,500-gallon pool? 

76. The temperature (in Fahrenheit) outside can be predicted by crickets using the rule, "Count the 
number of cricket chirps in 15 seconds and add 40." (i) Convert this expression to a function. Call it 
r(c), where T = temperature and c = number of chirps in 15 seconds. 

(ii) Graph this function. 

(iii) How many chirps would you expect to hear in 15 seconds if the temperature were 67°F? 

(iv) What does the y-intercept mean? 

(v) Are there values for which this graph would not predict well? Why? 



4.10 Chapter 4 Test 

Give the location of the following ordered pairs using the graph below. 



1. A 

2. B 

3. C 



• A 

1 

^ | 


• C 

|t 


-1 
-1 

< 


1 ** 

►B 

f 



4. Graph y = 5* -4. 

5. Find the slope between -3, 5) and (-1.25, -2.25). 

6. Find the intercepts of 6x + 9y = 54. 

7. In 2004, the high school graduation rate in the state of New Jersey was 86.3%. In 2008, the high 
school graduation rate in New Jersey was 84.6%. Determine the average rate of change. Use this 
information to make a conclusion regarding the graduation rate in New Jersey (source: http:// 
nces.ed.gov/pubs2010/2010341.pdf). 



167 



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8. Identify the slope and y-intercept of 4x + 7y = 28. 

9. Identify the slope and y-intercept of y = ^x - 8. 

10. Graph y = 9. 

11. Graph the line containing (3, 5) and (3, -7). What type of line have you created? 

12. The number of cups of milk is directly proportional to the number of quarts. If 26 quarts yields 104 
cups of milk, how many cups of milk is 2.75 quarts? 

13. Graph the direct variation situation using the table below: 






1 


2 


3 


4 


5 


6 


7 





2.25 


4.5 


6.75 


9 


11.25 


13.5 


15.75 



14. h varies directly as m when m = 4, h = 27. Find h when m = -5.5. 

15. h(n) = i|6 -n\ + 11; find h(25) 

16. Are these lines parallel? y = -2x + 1 and y = 2x - 1 

17. Mixture A has a 2% hydrogen solution and mixture B has a 1.5% hydrogen solution. How much of 
mixture B needs to be added to 6 ounces of mixture A to obtain a value of 0.51? 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/flexr/chapter/9614. 



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Chapter 5 

Writing Linear Equations 



You saw in the last chapter that linear graphs and equations are used to describe a variety of real-life 
situations. In mathematics, the goal is to find an equation that explains a situation as presented in a 
problem. In this way, we can determine the rule that describes the relationship. Knowing the equation or 
rule is very important since it allows us to find the values for the variables. There are different ways to 
find the best equation to represent a problem. The methods are based on the information you can gather 
from the problem. 

This chapter focuses on several formulas used to help write equations of linear situations, such as slope- 
intercept form, standard form, and point-slope form. This chapter also teaches you how to fit a line to 
data and how to use a fitted line to predict data. 

5.1 Linear Equations in Slope-Intercept Form 

Previously, you learned how to graph solutions to two-variable equations in slope-intercept form. This 
lesson focuses on how to write an equation for a graphed line. There are two things you will need from the 
graph to write the equation in slope-intercept form: 

1. The y-intercept of the graph 

2. The slope of the line 

Having these two pieces of information will allow you to make the appropriate substitutions in the slope- 
intercept formula. Recall from the last chapter, 

Slope-intercept form: y = (slope)x + (y - intercept) or y = mx + b 

Example 1: Write the equation for a line with a slope of 4 and a y-intercept (0, -3). 

Solution: Slope-intercept form requires two things: the slope and y-intercept. To write the equation, you 
substitute the values into the formula. 

y = (slope) x + (y - intercept) 

y = 4x+(-3) 
y = 4x - 3 

You can also use a graphed line to determine the slope and y-intercept. 
Example 2: Use the graph below to write its equation in slope-intercept form. 

169 www.ckl2.org 











i 

e 


^y 




















Jl 


/ 




















3 


/ 




















T 


/ 




















v 






















/ 












X 


ii -i 


■ -; 


i -: 


•■ ■' 


/, 


> 


: 


; ; 


i i 


■ « 


^ 








I 


2" 






















3 




















1 


o 


















1 


' 


■s- 















Solution: The y-intercept is (0, 2). Using the slope triangle, you can determine the slope is 
Substituting the value 2 for b and the value 3 for m, the equation for this line is y = 3x + 2. 



rise 
run 



z3 

-1 



Writing an Equation Given the Slope and a Point 

Sometimes it may be difficult to determine the y-intercept. Perhaps the y-intercept is rational instead of 
an integer. Maybe you don't know the y-intercept. All you have is the slope and an ordered pair. You 
can use this information to write the equation in slope-intercept form. To do so, you will need to follow 
several steps. 

Step 1: Begin by writing the formula for slope-intercept form y = mx + b. 

Step 2: Substitute the given slope for m. 

Step 3: Use the ordered pair you are given (x,y) and substitute these values for the variables x and y in 
the equation. 

Step 4: Solve for b (the y-intercept of the graph). 

Step 5: Rewrite the original equation in Step 1, substituting the slope for m and the y-intercept for b. 

Example 3: Write an equation for a line with slope of 4 that contains the ordered pair (-1, 5). 

Solution: 

Step 1: Begin by writing the formula for slope-intercept form. 



Step 2: Substitute the given slope for m. 



y = mx + b 



y = 4x + b 



Step 3: Use the ordered pair you are given (-1, 5) and substitute these values for the variables x and y in 
the equation. 

5 = (4)(-l) + * 

Step 4: Solve for b (the y-intercept of the graph). 

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5 = -4 + b 

5 + 4 = -4 + 4 + /? 
9 = Z? 

Step 5: Rewrite y = mx + /?, substituting the slope for m and the y-intercept for b. 

y = 4x + 9 

Example 4: Write the equation for a line with a slope of -3 containing the point (3, -5). 
Solution: Using the five-steps from above: 

y = (slope) x + (y - intercept) 

y = -3x + b 
-5 = -3(3) + Z7 
-5 = -9 + Z? 

4 = b 

y = -3x + 4 

Writing an Equation Given Two Points 

In many cases, especially real- world situations, you are given neither the slope nor the y-intercept. You 
might have only two points to use to determine the equation of the line. 

To find an equation for a line between two points, you need two things: 

1. The y-intercept of the graph 

2. The slope of the line 

Previously, you learned how to determine the slope between two points. Let's repeat the formula here. 

The slope between any two points (xi,yi) and (^2,^2) i s: slope = ^zj~- 

The procedure for determining a line given two points is the same five-step process as writing an equation 
given the slope and a point. 

Example 5: Write the equation for the line containing the points (3, 2) and (-2, 4)- 

Solution: You need the slope of the line. Find the line's slope by using the formula. Choose one ordered 
pair to represent (x\,yi) and the other ordered pair to represent (x2,j2)- 

y 2 -yi 4-2 2 



slope 



X2 - x\ -2-3 5 



Now use the five-step process to find the equation for this line. 
Step 1: Begin by writing the formula for slope-intercept form. 

y = mx + b 
Step 2: Substitute the given slope for m. 

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-2 

y = -—x + b 

5 

Step 3: Use one of the ordered pairs you are given (-2, 4) and substitute these values for the variables x 
and y in the equation. 

4 = I -? I (-2) + b 



Step 4: Solve for & (the y-intercept of the graph) 



4 
A=-+b 

5 

, 4 4 4 , 

5 5 5 

16 a 

Step 5: Rewrite y — mx + b, substituting the slope for m and the y-intercept for b. 

-2 16 

y =T x+ T 

Example 6: Write the equation for a line containing the points (-4, 1) and (-2, 3). 
Solution: 

1. Start with the slope-intercept form of the line y = mx + b. 

2. Find the slope of the line: m = y^r- = z^ZCTj = § = 1- 

3. Substitute the value of slope for m : y = (1)jc + b. 

4. Substitute the coordinate (-2, 3) into the equation for the variables x and y:3 = -2 + /?=>/? = 5. 

5. Rewrite the equation, substituting the slope for m and the y-intercept for b: y = x + 5. 

Writing a Function in Slope-Intercept Form 

Remember that a linear function has the form f(x) = mx + b. Here /(jc) represents the y values of the 
equation or the graph. So y = f(x) and they are often used interchangeably. Using the functional notation 
in an equation often provides you with more information. 

For instance, the expression f(x) = mx + b shows clearly that x is the independent variable because you 
substitute values of x into the function and perform a series of operations on the value of x in order to 
calculate the values of the dependent variable, y. 




In this case when you substitute x into the function, the function tells you to multiply it by m and then 
add b to the result. This process generates all the values of y you need. 

Example 7: Consider the function f{x) = 3x - 4. Find /(2),/(0), and /(-l). 

Solution: Each number in parentheses is a value of x that you need to substitute into the equation of the 
function. 

www.ckl2.org 172 



./(2) = 3(2)-4 = 6-4 = 2 ./(O) - 3(0) - 4 - 0-4 - -4 y^-1) = 3(-l) - 4 = -3 -4 = -7 

/(2) = 2;/(0) = -4; and /(-l) = -7 

Function notation tells you much more than the value of the independent variable. It also indicates a point 
on the graph. For example, in the above example, /(— 1) = -7. This means the ordered pair (-1, -7) is 
a solution to f(x) = 3x - 4 and appears on the graphed line. You can use this information to write an 
equation for a function. 

Example 8: Write an equation for a line with m = 3.5 and /(-2) = 1. 

Solution: You know the slope and you know a point on the graph (-2, 1). Using the methods presented 
in this lesson, write the equation for the line. 

Begin with slope-intercept form. 

y = mx + b 
Substitute the value for the slope. y = 3.5x + b 

Use the ordered pair to solve for b. 1 = 3.5 (-2) + b 

b = 8 
Rewrite the equation. y = 3.5x + 8 

or f(x) = 3.5x + 8 

Solve Real- World Problems Using Linear Models 

Let's apply the methods we just learned to a few application problems that can be modeled using a linear 
relationship. 

Example 9: Nadia has $200 in her savings account. She gets a job that pays $7.50 per hour and she deposits 
all her earnings in her savings account. Write the equation describing this problem in slope-intercept form. 
How many hours would Nadia need to work to have $500 in her account? 




Solution: Begin by defining the variables: 

y = amount of money in Nadia's savings account 

x = number of hours 

The problem gives the y-intercept and the slope of the equation. 

We are told that Nadia has $200 in her savings account, so b = 200. 

We are told that Nadia has a job that pays $7.50 per hour, so m = 7.50. 

By substituting these values in slope-intercept form y = mx + /?, we obtain y = 7.5x + 200. 

173 www.ckl2.org 



To answer the question, substitute $500 for the value of y and solve. 

500 = 7.5* + 200 => 7.5* = 300 => x = 40 



Nadia must work 40 hours if she is to have $500 in her account. 

Example 10: A stalk of bamboo of the family Phyllostachys nigra grows at steady rate of 12 inches per 
day and achieves its full height of 120 inches in 60 days. Write the equation describing this problem in 
slope-intercept form. How tall is the bamboo 12 days after it started growing? 

Solution: Define the variables. 

y = the height of the bamboo plant in inches 

x = number of days 

The problem gives the slope of the equation and a point on the line. 

The bamboo grows at a rate of 12 inches per day, so m = 12. 

We are told that the plant grows to 720 inches in 60 days, so we have the point (60, 720). 



Start with the slope-intercept form of the line. 

Substitute 12 for the slope. 

Substitute the point (60,720). 

Substitute the value of b back into the equation. 



y = mx + b 
y=12x + b 
720 = 12(60) +b 
y= 12* 



b = 



To answer the question, substitute the value x = 12 to obtain y = 12(12) = 144 inches. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Linear Equations in Slope-Intercept Form (14:58) 



Video 



Figure 5.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/757 



1. What is the formula for slope-intercept form? What do the variables m and b represent? 

2. What are the five steps needed to determine the equation of a line given the slope and a point on 
the graph (not the y-intercept)? 

3. What is the first step in finding the equation of a line given two points? 



www.ckl2.org 



174 



In 4 - 20, find the equation of the line in slope-intercept form. 



4. The line has slope of 7 and y-intercept of -2. 

5. The line has slope of -5 and y-intercept of 6. 

6. The line has slope = -2 and a y-intercept = 7. 

7. The line has slope = | and a y-intercept = |. 

8. The line has slope of -\ and contains point (4, -1). 

9. The line has slope of | and contains point ( \, lj. 

10. The line has slope of -1 and contains point (f 5 0j. 

11. The line contains points (2, 6) and (5, 0). 

12. The line contains points (5, -2) and (8, 4). 

13. The line contains points (3, 5) and (-3, 0). 

14. The slope of the line is -| and the line contains point (2, -2). 

15. The slope of the line is -3 and the line contains point (3, -5). 

16. The line contains points (10, 15) and (12, 20). 
17. 



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In 21 - 28, find the equation of the linear function in slope-intercept form. 



21. 

22. 
23. 

24. 
25. 
26. 

27. 
28. 



m = 5,/(0) = -3 

m = -2 and /(0) 



m = -7,/(2) = -l 
m=§,/(-l) = § 
m = 4.2,/(-3) = 7.1 

/(1.5) = -3,/(-l) = 2 
/(-l) = 1 and /(l) = -1 

29. To buy a car, Andrew puts in a down payment of $1500 and pays $350 per month in installments. 
Write an equation describing this problem in slope-intercept form. How much money has Andrew 
paid at the end of one year? 

30. Anne transplants a rose seedling in her garden. She wants to track the growth of the rose, so she 
measures its height every week. In the third week, she finds that the rose is 10 inches tall and in the 
eleventh week she finds that the rose is 14 inches tall. Assuming the rose grows linearly with time, 
write an equation describing this problem in slope-intercept form. What was the height of the rose 
when Anne planted it? 



www.ckl2.org 



176 



31. Ravi hangs from a giant exercise spring whose length is 5 m. When his child Nimi hangs from the 
spring, its length is 2 m. Ravi weighs 160 lbs. and Nimi weighs 40 lbs. Write the equation for this 
problem in slope-intercept form. What should we expect the length of the spring to be when his wife 
Amardeep, who weighs 140 lbs., hangs from it? 

32. Petra is testing a bungee cord. She ties one end of the bungee cord to the top of a bridge and to 
the other end she ties different weights. She then measures how far the bungee stretches. She finds 
that for a weight of 100 lbs., the bungee stretches to 265 feet and for a weight of 120 lbs., the bungee 
stretches to 275 feet. Physics tells us that in a certain range of values, including the ones given here, 
the amount of stretch is a linear function of the weight. Write the equation describing this problem 
in slope-intercept form. What should we expect the stretched length of the cord to be for a weight 
of 150 lbs? 

Mixed Review 

33. Translate into an algebraic sentence: One-third of a number is seven less than that number. 

34. The perimeter of a square is 67 cm. What is the length of its side? 

35. A hockey team played 17 games. They won two more than they lost. They lost 3 more than they 
tied. How many games did they win, lose, and tie? 

36. Simplify (30-4+4+2)+(2i+3) 

37. What is the opposite of 16.76? 

38. Graph the following on a number line: J6, ^-, -5.65, 4M. 

39. Simplify: [(-4 + 4.5) + (18 - | - 13|) + (-3.3)]. 

5.2 Linear Equations in Point- Slope Form 

Equations can be written in many forms. The last lesson taught you how to write equations of lines in 
slope-intercept form. This lesson will provide a second way to write an equation of a line: point-slope 
form. 

The line between any two points (xi,yi) and (^2,^2) can be written in the following equation: y - y± = 
m(x - jci). 

To write an equation in point-slope form, you need two things: 

1. The slope of the line 

2. A point on the line 

Example 1: Write an equation for a line containing (9, 3) and (4, 5). 
Solution: Begin by finding the slope. 

y 2 -yi 5-3 2 

slope = = = — 

%2 - x\ 4-9 5 

Instead of trying to find b (the y-intercept), you will use the point-slope formula. 

y-yi =m(x-xi) 
y-3=y(*-9) 



It doesn't matter which point you use. 



177 www.ckl2.org 



You could also use the other ordered pair to write the equation: 



y-5 = ^(x-4) 
5 



These equations may look completely different, but by solving each one for y, you can compare the slope- 
intercept form to check your answer. 



—2 —2 18 

y-3 = —(x-9)^y=—x+ — + 3 

-2 33 

y = T x+ T 

y-5 = ^(x-4) 
5 

-2 8 r 

,= T x+- + 5 

-2 33 

y = T x+ T 



This process is called rewriting in slope-intercept form. 

Example 2: Rewrite y — 5 = 3(x — 2) in slope-intercept form. 

Solution: Use the Distributive Property to simplify the right side of the equation. 

y - 5 = 3x - 6 
Solve for y: 



y -5 + 5 = 3x-6 + 5 
y = 3x - 1 



Graphing Equations Using Point-Slope Form 

If you are given an equation in point-slope form, it is not necessary to re- write it in slope-intercept form 
in order to graph it. The point-slope form of the equation gives you enough information so you can graph 
the line. 

Example 3: Make a graph of the line given by the equation y - 2 = |(jc + 2) 

Solution: Begin by rewriting the equation to make point-slope form: y-2 = %{x— (-2)) Now we see that 
point (-2, 2) is on the line and that the slope = |. First plot point (-2, 2) on the graph. 

www.ckl2.org 178 











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Writing a Linear Function in Point-Slope Form 

Remember from the previous lesson that f(x) and y are used interchangeably. Therefore, to write a function 
in point-slope form, you replace y -yi with f{x) -y\. 

Example 4: Write the equation of the linear function in point-slope form. 

m = 9.8 and /(5.5) = 12.5 

Solution: This function has a slope of 9.8 and contains the ordered pair (5.5, 12.5). Substituting the 
appropriate values into point-slope form, 

y - 12.5 = 9.8(jc- 5.5) 
Replacing y — yi with f(x) -yi, the equation becomes 



Solving Situations Involving Point-Slope Form 

Let's solve some word problems where point-slope form is needed. 

Example 5: Marciel rented a moving truck for the day. Marciel remembers only that the rental truck 
company charges $40 per day and some amount of cents per mile. Marciel drives 46 miles and the final 
amount of the bill (before tax) is $63. What is the amount per mile the truck rental company charges? 
Write an equation in point-slope form that describes this situation. How much would it cost to rent this 
truck if Marciel drove 220 miles? 




Solution: Define the variables: x = distance in miles; y = cost of the rental truck in dollars. There are 
two ordered pairs: (0, 40) and (46, 63). 

Step 1: Begin by finding the slope: ^^ = §§ = \. 

Step 2: Substitute the slope for m and one of the coordinates for (xi,yi). 

y _ 40 = I( x _o) 

To find out how much will it cost to rent the truck for 220 miles, substitute 220 for the variable x. 

v-40= -(220-0) 

v- 40 = 0.5(220) =>y = $150 

www.ckl2.org 180 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Linear Equations in Point-Slope Form (9:38) 




Figure 5.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/758 



1. What is the equation for a line containing the points (x\,yi) and (x2,y2) in point-slope form? 

2. In what ways is it easier to use point-slope form rather than slope-intercept form? 

Write the equation for the line in point-slope form. 



3. Slope is 

4. Slope is 

5. Slope is 

6. Slope is 

7. The line 

8. The line 

9. The line 

10. The line 

11. The line 

12. The line 

13. The line 



^; y-intercept -4. 

-jq and contains (10, 2). 

-75 and contains point (0, 125). 

10 and contains point (8, -2). 

contains points (-2, 3) and (-1, -2). 

contains the points (0, 0) and (1, 2). 

contains points (10, 12) and (5, 25). 

contains points (2, 3) and (0, 3). 

has slope | and y-intercept -3. 

has slope -6 and y-intercept 0.5. 

contains the points (-4, -2) and (8, 12). 



Write each equation in slope-intercept form. 

14. y-2 = 3(x-l) 

15. y + 4= f (jc + 6) 

16. = x + 5 

17. y=l(x- 24) 

In 18 - 25, write the equation of the linear function in point-slope form. 

18. m = -\ and /(0) = 7 

19. m = -12 and /(-2) = 5 

20. /(-7) = 5 and /(3) = -4 



181 



www.ckl2.org 



21. /(6) = and /(O) = 6 

22. m = 3 and /(2) = -9 

23. m = -§ and/(0) = 32 

24. m = 25 and /(O) = 250 

25. /(32) = and /(77) = 25 

26. Nadia is placing different weights on a spring and measuring the length of the stretched spring. She 
finds that for a 100 gram weight the length of the stretched spring is 20 cm and for a 300 gram weight 
the length of the stretched spring is 25 cm. Write an equation in point-slope form that describes this 
situation. What is the unstretched length of the spring? 

27. Andrew is a submarine commander. He decides to surface his submarine to periscope depth. It 
takes him 20 minutes to get from a depth of 400 feet to a depth of 50 feet. Write an equation in 
point-slope form that describes this situation. What was the submarine's depth five minutes after it 
started surfacing? 

28. Anne got a job selling window shades. She receives a monthly base salary and a $6 commission for 
each window shade she sells. At the end of the month, she adds up her sales and she figures out that 
she sold 200 window shades and made $2500. Write an equation in point-slope form that describes 
this situation. How much is Anne's monthly base salary? 

Mixed Review 

29. Translate into a sentence: 4(j + 2) = 400. 

30. Evaluate 0.45 • 0.25 - 24 -=■ \. 

31. The formula to convert Fahrenheit to Celsius is C(F) = ^fjp. What is the Celsius equivalent to 
35°F? 

32. Find the rate of change: The diver dove 120 meters in 3 minutes. 

33. What percent of 87.4 is 106? 

34. Find the percent of change: The original price was $25.00. The new price is $40.63. 

35. Solve for w: 606 = 0.045(w - 4000) + 0.07w. 

5.3 Linear Equations in Standard Form 

As the past few lessons of this chapter have shown, there are several ways to write a linear equation. This 
lesson introduces another method: standard form. You have already seen examples of standard form 
equations in a previous lesson. For example, here are some equations written in standard form. 

0.75(A) + 1.25(b) = 30 
7x-3y = 21 
2x + 3y = -6 

The standard form of a linear equation has the form Ax + By = C, where A, Z?, and C are integers and A 
and B are not both zero. 

Equations written in standard form do not have fractional coefficients and the variables are written on 
the same side of the equation. 

You should be able to rewrite any of the formulas into an alternate form. 

S lope - intercept form <-> S tandard form 
S lope - intercept form <-> Point - slope form 
Point - slope form <-> S tandard form 

www.ckl2.org 182 



Example 1: Rewrite |(/z) + |(fo) = 30 m standard form. 

Solution: According to the definition of standard form, the coefficients must be integers. So we need to 
clear the fractions of the denominator using multiplication. 

3 5 /3 5 \ , N 

-h + -b = 30 -> 4 -/* + -b = 4(30) 

4 4 \4 4 / 

3/z + 5Z7 = 120 

This equation is now in standard form, A = 3,5 = 5, and C = 120. 

Example 2: Rewrite y — 5 = 3(x — 2) in standard form. 

Solution: Use the Distributive Property to simplify the right side of the equation 

y - 5 = 3x - 6 

Rewrite this equation so the variables x and y are on the same side of the equation. 

y-5 + 6 = 3x-6 + 6 
y-y + l = 3x-y 

1 = 3x-y, where A=3, B=-l, and C=l. 

Example 3: Rewrite 5x - 7 = y in standard form. 

Solution: Rewrite this equation so the variables x and y are on the same side of the equation. 

5;t-7 + 7 = ;y + 7 
5x-y = y-y + 7 

5x - y = 7, where A=5, B=-l, and C=7. 

Finding Slope and y-Intercept of a Standard Form Equation 

Slope-intercept form and point-slope form of a linear equation both contain the slope of the equation 
explicitly, but the standard form does not. Since the slope is such an important feature of a line, it is 
useful to figure out how you would find the slope if you were given the equation of the line in standard 
form. 

Begin with standard form: Ax + By = C. 

If you rewrite this equation in slope-intercept form, it becomes: 

Ax- Ax + By = C - Ax 
By _ -Ax + C 

~B ~ B 

-A C 

y = — x -\ — 
y B B 

When you compare this form to slope-intercept form, y = mx + /?, you can see that the slope of a standard 
form equation is ^ and the y-intercept is ^. 

The standard form of a linear equation Ax + By = C has the following: 

slope = ^ and y - intercept = ^ . 

183 www.ckl2.org 



Example 4: Find the slope and y-intercept of 2x - 3y = -8. 
Solution: Using the definition of standard form, A = 2,B = -3, and C 



slope = 


-A 
~B~ ~ 


-2 
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2 

"* 3 


intercept — 


C 


-8 


8 



B -3 



The slope is | and the y-intercept is |. 



Applying Standard Form to Real- World Situations 

Example 5: Nimitha buys fruit at her local farmer's market. This Saturday, oranges cost $2 per pound 
and cherries cost $3 per pound. She has $12 to spend on fruit. Write an equation in standard form that 
describes this situation. If she buys 4 pounds of oranges, how many pounds of cherries can she buy? 




Solution: Define the variables: x = pounds of oranges and y = pounds of cherries. 

The equation that describes this situation is: 2x + 3y = 12 

If she buys 4 pounds of oranges, we substitute x = 4 in the equation and solve for y. 

2(4) +3y=12=>3y=12-8=>3y = 4=>y=!. Nimitha can buy l| pounds of cherries. 

Example 6: Jethro skateboards part of the way to school and walks for the rest of the way. He can 
skateboard at 7 miles per hour and he can walk at 3 miles per hour. The distance to school is 6 miles. 
Write an equation in standard form that describes this situation. If Jethro skateboards for - an hour, how 
long does he need to walk to get to school? 




Solution: Define the variables: x = hours Jethro skateboards and y = hours Jethro walks. 
The equation that describes this situation is 7x + 3y = 6. 

If Jethro skateboards \ hour, we substitute x = 0.5 in the equation and solve for y. 

£ — qp;^q^ — o ^ ^ ^ — _ ,,_., I1111 ^ l w -i, ... - 

g. UCL111U IHUDI VVCMJY g 



7(0.5) + 3y = 6 => 3y = 6 - 3.5 => 3y = 2.5 => y = |. Jethro must walk | of an hour. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 

www.ckl2.org 184 



number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Linear Equations in Standard Form (10:08) 




Figure 5.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/759 



1. What is the standard form of a linear equation? What do A, B 1 and C represent? 

2. What is the meaning of "clear the fractions"? How would you go about doing so? 

3. Consider the equation Ax + By = C. What are the slope and y-intercept of this equation? 

Rewrite the following equations in standard form. 

4. y = 3jk-8 

5. y = -x- 6 

6. y = |x-4 

7. 0.30jc + 0.70y = 15 

8. 5 = \x-y 

9. - y _7 = _5( x _i2) 
10. 2y = 6x + 9 

12. y+ ! = §(*- 2) 

13. 3y + 5 = 4(x-9) 

Find the slope and y-intercept of the following lines. 

14. 5x-2y= 15 

15. 3jt + 6y = 25 

16. x-8y = 12 

17. 3x-7y = 20 

18. 9jt-9y = 4 

19. 6x + y = 3 

20. x-y = 9 

21. 8x + 3y= 15 

22. 4jt + 9y = 1 

In 23 - 27, write each equation in standard form by first writing it in point-slope form. 



23. Slope = -1 through point (-3, 5) 



24. Slope 



through point (4, 0) 



185 



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25. Line through (5, -2) and (-5, 4) 

26. Line through (-3, -2) and (5, 1) 

27. Line through (1, -1) and (5, 2) 

28. The farmer's market sells tomatoes and corn. Tomatoes are selling for $1.29 per pound and corn is 
selling for $3.25 per pound. If you buy 6 pounds of tomatoes, how many pounds of corn can you buy 
if your total spending cash is $11.61? 

29. The local church is hosting a Friday night fish fry for Lent. They sell a fried fish dinner for $7.50 
and a baked fish dinner for $8.25. The church sold 130 fried fish dinners and took in $2,336.25. How 
many baked fish dinners were sold? 

30. Andrew has two part-time jobs. One pays $6 per hour and the other pays $10 per hour. He wants to 
make $366 per week. Write an equation in standard form that describes this situation. If he is only 
allowed to work 15 hours per week at the $10 per hour job, how many hours does he need to work 
per week at his $6 per hour job in order to achieve his goal? 

31. Anne invests money in two accounts. One account returns 5% annual interest and the other returns 
7% annual interest. In order not to incur a tax penalty, she can make no more than $400 in interest 
per year. Write an equation in standard form that describes this problem. If she invests $5000 in the 
5% interest account, how much money does she need to invest in the other account? 

Mixed Review 

32. Write the following equation in slope-intercept form: y - 2 = 6(x - 3). 

33. Solve for p: *=? = £+1. 

34. Describe the graph x = 1.5. 

35. Tell whether (4, -3) is a solution to 5x + 3y = 9. 

36. Give the coordinates of a point located in quadrant III. 

37. Find the slope between (6, 6) and (16, 6). 

38. Graph the equation y = |x - 7. 

5.4 Equations of Parallel and Perpendicular Lines 

In a previous lesson, you learned how to identify parallel lines. 

Parallel lines have the same slope. 

Each of the graphs below have the same slope. According to the definition, all these lines are parallel. 




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186 



Example 1: Are y = \x - 4 and -3x + 9y = 18 parallel? 

Solution: The slope of the first line is g. Any line parallel to this must also have a slope of \. 

Find the slope of the second equation: A = -3, B = 9 

-A 3 1 
slope = — = > - 

These two lines have the same slope so they are parallel. 

Slopes of Perpendicular Lines 

Lines can be parallel, coincident (overlap each other), or intersecting (crossing). Lines that intersect at 
90° angles have a special name: perpendicular lines. The slopes of perpendicular lines have a special 
property. 

Perpendicular lines form a right angle. The product of their slopes is -1. 

mi - rri2 = -1 

Example 2: Verify that the following lines are perpendicular. 
Line a: passes through points (-2, -7) and (1, 5) 
Line b: passes through points (4, 1) and (-8, 4) 
Solution: Find the slopes of each line. 

5 -(-7) 12 4 4-13-1 
Line a : ; — - = — = - Line b : = = — 

l-(-2) 3 1 -8-4 -12 4 

To verify that the lines are perpendicular, the product of their slopes must equal -1. 

4 -1 

Because the product of their slopes is -1, lines a and b are perpendicular. 
Example 3: Determine whether the two lines are parallel, perpendicular, or neither: 
Line 1: 2x = y - 10; Line 2: y = -2x + 5 
Solution: Begin by finding the slopes of lines 1 and 2. 

2x+10 = y-10 + 10 
2x+10 = y 



The slope of the first line is 2. 



y = -2X+5 



The slope of the second line is -2. 

These slopes are not identical, so these lines are not parallel. 

To check if the lines are perpendicular, find the product of the slopes. 2 x -2 = -4. The product of the 
slopes is not -1, so the lines are not perpendicular. 

Lines 1 and 2 are neither parallel nor perpendicular. 

187 www.ckl2.org 



Writing Equations of Parallel Lines 

Example 4: Find the equation parallel to the line y = 6x - 9 passing through (-1, 4)- 

Solution: Parallel lines have the same slope, so the slope will be 6. You have a point and the slope, so 
you can use point-slope form. 

y-yi =m(x-xi) 
y-4 = 6(jc+ 1) 

You could rewrite it in slope-intercept form: 

y = Q X + 6 + 4 
y = Q X + 10 

Writing Equations of Perpendicular Lines 

Writing equations of perpendicular lines is slightly more difficult than writing parallel line equations. The 
reason is because you must find the slope of the perpendicular line before you can proceed with writing an 
equation. 

Example: Find the equation perpendicular to the line y = — 3jc + 5 that passes through point (2, 6). 

Solution: Begin by finding the slopes of the perpendicular line. Using the perpendicular line definition, 
m\ - m2 = -1. The slope of the original line is -3. Substitute that for mi. 

-3 • rri2 = -1 

Solve for m2, the slope of the perpendicular line. 

-3rri2 -1 

-3 = ^3 

1 



"2=3 

The slope of the line perpendicular to y = -3x + 5 is i. 

You now have the slope and a point. Use point-slope form to write its equation. 

y-Q= l -{ X -2) 

You can rewrite this in slope-intercept form: y — \x - I + 6. 

1 16 

y =s x+ T 

Example 4: Find the equation of the line perpendicular to the line y = 5 and passing through (5, 4)- 

Solution: The line y = 5 is a horizontal line with slope of zero. The only thing that makes a 90° angle 
with a horizontal line is a vertical line. Vertical lines have undefined slopes. 

Since the vertical line must go through (5, 4), the equation is x = 5. 

Multimedia Link: For more help with writing lines, visit AlgebraLab. 

www.ckl2.org 188 



Families of Lines 



A straight line has two very important properties, its slope and its y-intercept. The slope tells us how 
steeply the line rises or falls, and the y-intercept tells us where the line intersects the y-axis. In this 
section, we will look at two families of lines. 

A family of lines is a set of lines that have something in common with each other. Straight lines can 
belong to two types of families: where the slope is the same and where the y-intercept is the same. 



Family 1: The slope is the same 



Remember that lines with the same slope are parallel. Each line on the Cartesian plane below has an 
identical slope with different y-intercepts. All the lines look the same but they are shifted up and down 
the y-axis. As b gets larger the line rises on the y-axis and as b gets smaller the line goes lower on the 
y-axis. This behavior is often called a vertical shift. 





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The graph below shows several lines with the same y-intercept but varying slopes. 



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Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Equations of Parallel and Perpendicular Lines (9:13) 




Figure 5.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/760 



1. Define parallel lines. 

2. Define perpendicular lines. 

3. What is true about the slopes of perpendicular lines? 

4. What is a family of lines? 

Determine the slope of a line a) parallel and b) perpendicular to each line given. 



5. y = -5x + 7 

6. 2x + 8y = 9 

7. x = 8 

8. y = -4.75 

9. y-2 = Ux + 3) 



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190 



In 9 - 16, determine whether the lines are parallel, perpendicular, or neither. 



10. Line 

11. Line 
6). 

12. Line 
5). 

13. Line 

4). 

14. Line 

15. Line 

16. Line 

17. Find 

18. Find 

19. Find 

20. Find 

21. Find 

22. Find 



a : passing through points (-1, 4) and (2, 6); Line b : passing through points (2, -3) and (8, 1). 
a : passing through points (4, -3) and (-8, 0); Line b : passing through points (-1, -1) and (-2, 

a : passing through points (-3, 14) and (1, -2); Line b : passing through points (0, -3) and (-2, 

a : passing through points (3, 3) and (-6, -3); Line b : passing through points (2, -8) and (-6, 

1: 4y + x = 8; Line 2: 12y + 3x = 1 

1: 5y + 3x + 1; Line 2: 6y + lOx = -3 

1: 2y - 3x + 5 = 0; Line 2: y + 6x = -3 

the equation of the line parallel to 5x - 2y = 2 that passes through point (3, -2). 

the equation of the line perpendicular to y = -|x - 3 that passes through point (2, 8). 

the equation of the line parallel to 7y + 2x - 10 = that passes through the point (2, 2). 

the equation of the line perpendicular to y + 5 = 3(jc - 2) that passes through the point (6, 2). 

the equation of the line through (2, -4) perpendicular to y = Sx + 3. 

the equation of the line through (2, 3) parallel to y = |x + 5. 



In 23 - 26, write the equation of the family of lines satisfying the given condition. 



0. 



23. All lines pass through point (0, 4). 

24. All lines are perpendicular to 4x + 3y - 1 

25. All lines are parallel to y - 3 = 4x + 2. 

26. All lines pass through point (0, -1). 

27. Write an equation for a line parallel to the equation graphed below. 

28. Write an equation for a line perpendicular to the equation graphed below and passing through the 
ordered pair (0, -1). 











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Mixed Review 

29. Graph the equation 2x - y = 10. 

30. On a model boat, the stack is 8 inches high. The actual stack is 6 feet tall. How tall is the mast on 
the model if the actual mast is 40 feet tall? 



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31. The amount of money charged for a classified advertisement is directly proportional to the length 
of the advertisement. If an 50- word advertisement costs $11.50, what is the cost of a 70- word 
advertisement? 

32. Simplify VTT2. 

33. Simplify Vl2 2 -7 2 . 

34. Is v3 - v2 rational, irrational, or neither? Explain your answer. 

35. Solve for s: 15^ = 6(^ + 32). 



Quick Quiz 

1. Write an equation for a line with slope of | and y-intercept (0, 8). 

2. Write an equation for a line containing (6, 1) and (7, -3). 

3. A plumber charges $75 for a 2.5-hour job and $168.75 for a 5-hour job. 

Assuming the situation is linear, write an equation to represent the plumber's charge and use it to predict 
the cost of a 1-hour job. 

4. Rewrite in standard form: y = |jc + 11. 

5. Sasha took tickets for the softball game. Student tickets were $3.00 and adult tickets were $3.75. She 
collected a total of $337.50 and sold 75 student tickets. How many adult tickets were sold? 



5.5 Fitting a Line to Data 



The real- world situations you have been studying so far form linear equations. However, most data in life 
is messy and does not fit a line in slope-intercept form with 100% accuracy. Because of this tendency, 
people spend their entire career attempting to fit lines to data. The equations that are created to fit the 
data are used to make predictions, as you will see in the next lesson. 

This lesson focuses on graphing scatter plots and using the scatter plot to find a linear equation that will 
best fit the data. 

A scatter plot is a plot of all the ordered pairs in the table. This means that a scatter plot is a relation, 
and not necessarily a function. Also, the scatter plot is discrete, as it is a set of distinct points. Even 
when we expect the relationship we are analyzing to be linear, we should not expect that all the points 
would fit perfectly on a straight line. Rather, the points will be "scattered" about a straight line. There are 
many reasons why the data does not fall perfectly on a line. Such reasons include measurement errors 
and outliers. 

Measurement error is the amount you are off by reading a ruler or graph. 

An outlier is a data point that does not fit with the general pattern of the data. It tends to be "outside" 
the majority of the scatter plot. 

Example: Make a scatter plot of the following ordered pairs. 

(0, 2), (1, 4.5), (2, 9), (3, 11), (4, 13), (5, 18), (6, 19.5) 

Solution: Graph each ordered pair on one Cartesian plane. 

www.ckl2.org 192 



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Fitting a Line to Data 

Notice that the points graphed on the plane above look like they might be part of a straight line, although 
they would not fit perfectly. If the points were perfectly lined up, it would be quite easy to draw a line 
through all of them and find the equation of that line. However, if the points are "scattered," we try to 
find a line that best fits the data. The graph below shows several potential lines of best fit. 




You see that we can draw many lines through the points in our data set. These lines have equations that 
are very different from each other. We want to use the line that is closest to all the points on the graph. 
The best candidate in our graph is the red line A. Line A is the line of best fit for this scatter plot. 

Writing Equations for Lines of Best Fit 

Once you have decided upon your line of best fit, you need to write its equation by finding two points on 
it and using either: 

• Point-slope form; 



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• Standard form; or 

• Slope-intercept form. 

The form you use will depend upon the situation and the ease of finding the y-intercept. 
Using the red line from the example above, locate two points on the line. 




Find the slope: m = ^p = ¥ = 3 - 25 - 

Then y = 3.25* + b. 

Substitute (3, 11) into the equation. 11 = 3.25(3) + b => b = 1.25 

The equation for the line that fits the data best is y = 3.25.x + 1.25. 



Finding Equations for Lines of Best Fit Using a Calculator 

Graphing calculators can make writing equations of best fit easier and more accurate. Two people working 
with the same data might get two different equations because they would be drawing different lines. To 
get the most accurate equation for the line, we can use a graphing calculator. The calculator uses a 
mathematical algorithm to find the line that minimizes error between the data points and the line of best 
fit. 

Example: Use a graphing calculator to find the equation of the line of best fit for the following data: (3, 
12), (8, 20), (1, 7), (10, 23), (5, 18), (8, 24), (11, 30), (2, 10). 

Solution: 

Step 1: Input the data in your calculator. Press [STAT] and choose the [EDIT] option. 



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Input the data into the table by entering the x values in the first column and the y values in the second 
column. 

Step 2: Find the equation of the line of best fit. 



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Press [STAT] again and use the right arrow to select [CALC] at the top of the screen. 

Chose option number 4: LinReg(ax + b) and press [ENTER]. The calculator will display LinReg(ax + b). 



LinRe9 
y=ax+b 
a=2.81 
b=5.94 



Press [ENTER] and you will be given the a and b values. 

Here a represents the slope and b represents the y-intercept of the equation. The linear regression line is 
y = 2.01jc + 5.94. 

Step 3: Draw the scatter plot. 



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To draw the scatter plot press [STATPLOT] [2nd] [Y=]. 

Choose Plot 1 and press [ENTER]. 

Press the On option and choose the Type as scatter plot (the one highlighted in black). 

Make sure that the X list and Y list names match the names of the columns of the table in Step 1. 



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Choose the box or plus as the mark since the simple dot may make it difficult to see the points. 

Press [GRAPH] and adjust the window size so you can see all the points in the scatter plot. 

Step 4: Draw the line of best fit through the scatter plot. 

Press [Y=]. 

Enter the equation of the line of best fit that you just found: Y\ = 2.0 IX + 5.94. 

Press [GRAPH]. 




Using Lines of Best Fit to Solve Situations 

Example: Gal is training for a 5K race (a total of 5000 meters, or about 3.1 miles). The following table 
shows her times for each month of her training program. Assume here that her times will decrease in a 
straight line with time. Find an equation of a line of fit. Predict her running time if her race is in August. 




Table 5.1: 



Month 



Month number 



Average time (minutes) 



January 
February 
March 
April 




1 
2 
3 



40 

38 
39 

38 



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196 



Table 5.1: (continued) 



Month 



Month number 



Average time (minutes) 



May 
June 



4 

5 



33 
30 



Solution: Begin by making a scatter plot of Gal's running times. The independent variable, jc, is the month 
number and the dependent variable, y, is the running time in minutes. Plot all the points in the table on 
the coordinate plane. 



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Draw a line of fit. 

Choose two points on the line (0, 41) and (4, 34). 

Find the equation of the line. 



_ 34-41 __7 _ 3 

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7 
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7 
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4 V y 

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y = --x + 41 

4 



In a real- world problem, the slope and y-intercept have a physical significance. 



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Since the slope is negative, the number of minutes Gal spends running a 5K race decreases as the months 
pass. The slope tells us that Gal's running time decreases 1.75 minutes per month. 

The y-intercept tells us that when Gal started training, she ran a distance of 5K in 41 minutes, which is 
just an estimate, since the actual time was 40 minutes. 

The problem asks us to predict Gal's running time in August. Since June is assigned to month number 
five, then August will be month number seven. Substitute x = 7 into the line of best fit equation. 



y : 



-(7) + 41 



49 



+ 41 



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28- 



The equation predicts that Gal will be running the 5K race in 28.75 minutes. 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Fitting a Line to Data (7:48) 



Video 



Figure 5.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/762 



www.ckl2.org 



198 



1. What is a scatter plot? How is this different from other graphs you have created? 

2. Define line of best fit. 

3. What is an outlier? How can an outlier be spotted on a graph? 

4. What are the two methods of finding a line of best fit? 

5. Explain the steps needed to find a line of best fit "by hand." What are some problems with using 
this method? 

For each data set, draw the scatter plot and find the equation of the line of best fit by hand. 

6. (57, 45) (65, 61) (34, 30) (87, 78) (42, 41) (35, 36) (59, 35) (61, 57) (25, 23) (35, 34) 

7. (32, 43) (54, 61) (89, 94) (25, 34) (43, 56) (58, 67) (38, 46) (47, 56) (39, 48) 

8. (12, 18) (5, 24) (15, 16) (11, 19) (9, 12) (7, 13) (6, 17) (12, 14) 

9. (3, 12) (8, 20) (1, 7) (10, 23) (5, 18) (8, 24) (2, 10) 

In 10 - 12, for each data set, use a graphing calculator to find the equation of the line of best fit. 

10. (57, 45) (65, 61) (34, 30) (87, 78) (42, 41) (35, 36) (59, 35) (61, 57) (25, 23) (35, 34) 

11. (32, 43) (54, 61) (89, 94) (25, 34) (43, 56) (58, 67) (38, 46) (47, 56) (95, 105) (39, 48) 

12. (12, 18) (3, 26) (5, 24) (15, 16) (11, 19) (0, 27) (9, 12) (7, 13) (6, 17) (12, 14) 

13. Shiva is trying to beat the samosa eating record. The current record is 53.5 samosas in 12 minutes. 
The following table shows how many samosas he eats during his daily practice for the first week of 
his training. Will he be ready for the contest if it occurs two weeks from the day he started training? 
What are the meanings of the slope and the y-intercept in this problem? 

Table 5.2: 

Day No. of Samosas 

1 30 

2 34 

3 36 

4 36 

5 40 

6 43 

7 45 



14. Nitisha is trying to find the elasticity coefficient of a Superball. She drops the ball from different 
heights and measures the maximum height of the resulting bounce. The table below shows her data. 
Draw a scatter plot and find the equation. What is the initial height if the bounce height is 65 cm? 
What are the meanings of the slope and the y-intercept in this problem? 

Table 5.3: 

Initial height (cm) Bounce height (cm) 

30 22 

35 26 

40 29 

45 34 



199 www.ckl2.org 



Table 5.3: (continued) 



Initial height (cm) Bounce height (cm) 

50 38 

55 40 

60 45 

65 50 

70 52 



15. Baris is testing the burning time of "BriteGlo" candles. The following table shows how long it takes 
to burn candles of different weights. Let's assume it's a linear relation. We can then use a line to fit 
the data. If a candle burns for 95 hours, what must be its weight in ounces? 

Table 5.4: Candle Burning Time Based on Candle Weight 



Candle weight (oz) Time (hours) 



2 15 

3 20 

4 35 

5 36 
10 80 
16 100 
22 120 
26 180 



16. The table below shows the median California family income from 1995 to 2002 as reported by the 
U.S. Census Bureau. Draw a scatter plot and find the equation. What would you expect the median 
annual income of a Californian family to be in year 2010? What are the meanings of the slope and 
the y— intercept in this problem? 



Table 5.5: 



Year Income 



1995 53,807 

1996 55,217 

1997 55,209 

1998 55,415 

1999 63,100 

2000 63,206 

2001 63,761 

2002 65,766 



Mixed Review 

17. Sheri bought an espresso machine and paid $119.64 including tax. The sticker price was $110.27. 
What was the percent of tax? 



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18. What are the means of - = -go-? What are the extremes? 

19. Solve the proportion in question 18. 

20. The distance traveled varies directly with the time traveled. If a car has traveled 328.5 miles in 7.3 
hours, how many hours will it take to travel 82.8 miles? 

21. Evaluate t(x) = 0.85x when x = 6015. 



5.6 Predicting with Linear Models 

Numerical information appears in all areas of life. You can find it in newspapers, in magazines, in journals, 
on the television, or on the Internet. In the last lesson, you saw how to find the equation of a line of best 
fit. Using a line of best fit is a good method if the relationship between the dependent and independent 
variables is linear. Not all data fits a straight line, though. This lesson will show other methods to help 
estimate data values. These methods are useful in both linear and non-linear relationships. 



Linear Interpolation 

Linear interpolation is useful when looking for a value between given data points. It can be considered 
as "filling in the gaps" of a table of data. 

The strategy for linear interpolation is to use a straight line to connect the known data points on either 
side of the unknown point. Linear interpolation is often not accurate for non-linear data. If the points in 
the data set change by a large amount, linear interpolation may not give a good estimate. 



Linear Extrapolation 

Linear extrapolation can help us estimate values that are either higher or lower than the values in the data 
set. Think of this as "the long-term estimate" of the data. 

The strategy for linear extrapolation is to use a subset of the data instead of the entire data set. This is 
especially true for non-linear data you will encounter in later chapters. For this type of data, it is sometimes 
useful to extrapolate using the last two or three data points in order to estimate a value higher than the 
data range. 



Collecting and Organizing Data 

Data can be collected through various means, including surveys or experiments. 

A survey is a data collection method used to gather information about individuals' opinions, beliefs, or 
habits. 

The information collected by the U.S. Census Bureau or the Center for Disease Control are examples of 
data gathered using surveys. The U.S. Census Bureau collects information about many aspects of the U.S. 
population. 

An experiment is a controlled test or investigation. 

Let's say we are interested in how the median age for first marriages has changed during the 20^ century. 
The U.S. Census provides the following information about the median age at first marriage for males and 
females. Below is the table of data and its corresponding scatter plot. 

201 www.ckl2.org 




Table 5.6: 



Year 



Median Age of Males 



Median Age of Females 



1890 
1900 
1910 
1920 
1930 
1940 
1950 
1960 
1970 
1980 
1990 
2000 



26.1 
25.9 
25.1 
24.6 
24.3 
24.3 
22.8 
22.8 
23.2 
24.7 
26.1 
26.8 



22.0 
21.9 
21.6 
21.2 
21.3 
21.5 
20.3 
20.3 
20.8 
22.0 
23.9 
25.1 



Median Age of Males and Females at First Marriage by Year 





















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Example: Estimate the median age for the first marriage of a male in the year 1946. 

Solution: We will first use the method of interpolation because there is a "gap" needing to be filled. 1946 
is between 1940 and 1950, so these are the data points we will use. 



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1900 1920 1940 1960 1980 2000 
year 

By connecting the two points, an equation can be found. 



Slope 



22.8 - 24.3 



-1.5 



m = 



Equation 



1950 - 1940 10 
y = -0.15x + Z? 

24.3 = -0.15(1940) + b 

b = 315.3 

y = -0.15x + 315.3 



= -0.15 



To estimate the median age of marriage of males in year 1946, substitute x = 1946 in the equation. 

y = -0.15(1946) + 315.3 = 23.4 years old 

Example: The Center for Disease Control (CDC) has the following information regarding the percentage of 
pregnant women smokers organized by year. Estimate the percentage of pregnant women that were smoking 
in the year 1998. 

Table 5.7: Percent of Pregnant Women Smokers by Year 



Year 



Percent 



1990 
1991 
1992 
1993 
1994 
1995 
1996 
2000 
2002 
2003 
2004 



18.4 
17.7 
16.9 
15.8 
14.6 
13.9 
13.6 
12.2 
11.4 
10.4 
10.2 



Percent of Pregnant Women Smokers by Year 

203 



www.ckl2.org 



y 


-30 
















































s 

5-20 

r •< 

S ^- 
















• 














1 


- -1 A 




1 
• 


» 


< 


• * 

• 







- 1U 












" 




















I 


- 5 




























X 




1 1 1 1 1 j 1 1_^ 



1992 1994 1996 1998 2000 2002 2004 
year 



Solution: We want to use the information close to 1998 to interpolate the data. We do this by connecting 
the points on either side of 1998 with a straight line and find the equation of that line. 



Slope 



12.2-13.6 -1.4 



m = 



Equation 



2000 - 1996 
y = -0.35jc + Z? 

12.2 = -0.35(2000) +b 

b = 712.2 

y = -0.35x + 712.2 



= -0.35 



To estimate the percentage of pregnant women who smoked in year 1998, substitute x = 1998 into the 
equation. 

y = -0.35(1998) + 712.2 = 12.9% 



Predicting Using an Equation 

When linear interpolation and linear extrapolation do not produce accurate predictions, using the line of 
best fit (linear regression) may be the best choice. The "by hand" and calculator methods of determining 
the line of best fit were presented in the last lesson. 

Example: The winning times for the women's 100-meter race are given in the following table. Estimate 
the winning time in the year 2010. Is this a good estimate? 











Table 5.8: 








Winner 


Ctry. 


Year 


Seconds Winner 


Ctry. 


Year 


Seconds 


Mary 


UK 


1922 


12.8 


Vera 


Sov. 


1958 


11.3 


Lines 








Krepkina 








Leni 


Germ. 


1925 


12.4 


Wyomia 


USA 


1964 


11.2 


Schmidt 








Tyus 








Gertrurd 


Germ. 


1927 


12.1 


Barbara 


USA 


1968 


11.1 


Glasitsch 








Ferrell 








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204 









Table 5.8: (continued) 



Winner 


Ctry. 


Year 


Seconds 


Winner 


Ctry. 


Year 


Seconds 


Tollien 


Neth. 


1930 


12.0 


Ellen 


E. Germ. 


1972 


11.0 


Schuur- 








Strophal 








man 
















Helen 


USA 


1935 


11.8 


Inge Hel- 


W. Germ. 


1975 


11.0 


Stephens 








ten 








Lulu Mae 


USA 


1939 


11.5 


Marlies 


E. Germ. 


1982 


10.9 


Hymes 








Gohr 








Fanny 


Neth. 


1943 


11.5 


Florence 


USA 


1988 


10.5 


Blankers- 








Griffith 








Koen 








Joyner 








Marjorie 


Austr. 


1952 


11.4 










Jackson 

















Solution: Start by making a scatter plot of the data. Connect the last two points on the graph and find 
the equation of the line. 

Winning Times for the Women's 100-meter Race by Year 

3 Source: http : //en . wikipedia . org/wiki/World_Record_progression_100_m_women. 



-8' 

O 



- IU 

14 
























I *4 

-12 
-10 
-8 
-6 


V 






















-1 


'*< 


* 


• • 


** 


•• 




























f 




















21 


310 




-4- 














































X 



1990 1920 1940 1960 1980 20( 
Year 

Slope 



10.5-10.9 



-0.4 



m = 



Equation 



1988 - 1982 6 

y = -0.067x + b 

10.5 = -0.067(1988) + b 

b = 143.7 

y = -0.067x + 143.7 



= -0.067 



The winning time in year 2010 is estimated to be: y = -0.067(2010) + 143.7 = 9.03 seconds . 

How accurate is this estimate? It is likely that it's not very accurate because 2010 is a long time from 1988. 
This example demonstrates the weakness of linear extrapolation. Estimates given by linear extrapolation 
are never as good as using the equation from the line of best fit method. In this particular example, the 



205 



www.ckl2.org 



last data point clearly does not fit in with the general trend of the data so the slope of the extrapolation 
line is much steeper than it should be. 

As a historical note, the last data point corresponds to the winning time for Florence Griffith Joyner in 
1988. After her race, she was accused of using performance-enhancing drugs but this fact was never proven. 
In addition, there is a question about the accuracy of the timing because some officials said that the tail 
wind was not accounted for in this race even though all the other races of the day were impacted by a 
strong wind. 

Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Predicting with Linear Models (11:46) 



Video 



Figure 5.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/764 



1. What does it mean to interpolate the data! In which cases would this method be useful? 

2. How is interpolation different from extrapolation? In which cases would extrapolation be more 
beneficial? 

3. What was the problem with using the interpolation method to come up with an equation for the 
women's Olympic winning times? 

4. Use the Winning Times data and determine an equation for the line of best fit. 

5. Use the Median Age at First Marriage data to estimate the age at marriage for females in 1946. 
Fit a line, by hand, to the data before 1970. 

6. Use the Median Age at First Marriage data to estimate the age at marriage for females in 1984. 
Fit a line, by hand, to the data from 1970 on in order to estimate this accurately. 

7. Use the Median Age at First Marriage data to estimate the age at marriage for males in 1995. 
Use linear interpolation between the 1990 and 2000 data points. 

8. Use the data from Pregnant Women and Smoking to estimate the percent of pregnant smokers 
in 1997. Use linear interpolation between the 1996 and 2000 data points. 

9. Use the data from Pregnant Women and Smoking to estimate the percent of pregnant smokers 
in 2006. Use linear extrapolation with the final two data points. 

10. Use the Winning Times data to estimate the winning time for the female 100-meter race in 1920. 
Use linear extrapolation because the first two or three data points have a different slope than the 
rest of the data. 

11. The table below shows the highest temperature vs. the hours of daylight for the 15^ day of each 
month in the year 2006 in San Diego, California. Using linear interpolation, estimate the high 
temperature for a day with 13.2 hours of daylight. 



www.ckl2.org 



206 



Table 5.9: 



Hours of daylight High temperature (F) 

10.25 60 

11.0 62 

12 62 

13 66 
13.8 68 

14.3 73 

14 86 

13.4 75 
12.4 71 

11.4 66 

10.5 73 
10 61 

12. Use the table above to estimate the high temperature for a day with 9 hours of daylight using linear 
extrapolation. Is the prediction accurate? Find the answer using line of best fit. 

5.7 Problem- Solving Strategies: Use a Linear Model 

This chapter has focused on writing equations and determining lines of best fit. When we fit a line to data 
using interpolation, extrapolation, or linear regression, it is called linear modeling. 

A model is an equation that best describes the data graphed in the scatter plot. 

Example 1: Dana heard something very interesting at school Her teacher told her that if you divide 
the circumference of a circle by its diameter you always get the same number. She tested this statement 
by measuring the circumference and diameter of several circular objects. The following table shows her 
results. 

From this data, estimate the circumference of a circle whose diameter is 12 inches. What about 25 inches? 
60 inches? 

Solution: Begin by creating a scatter plot and drawing the line of best fit. 

Table 5.10: Diameter and Circumference of Various Objects 

Object Diameter (inches) Circumference (inches) 

Table 53 170 

Soda can 2.25 7.1 

Cocoa tin 4.2 12.6 

Plate 8 25.5 

Straw 0.25 1.2 

Propane tank 13.3 39.6 

Hula hoop 34.25 115 



207 www.ckl2.org 



CO 

•Si 
o 

e 
e 

o 



-200 
-175 

- 1RO 


























-125 














-100 














- 7R 














- RH 














-OR ^ 












"ZD/* 












X 



20 30 40 
diameter (inches) 



60 



Find the equation of the line of best fit using points (0.25, 1.2) and (8, 25.5). 



Slope 



Equation 



25.5 - 12 24.3 



m — 



7.75 



= 3.14 



8-0.25 
y = 3.14x + & 

1.2 = 3.14(0.25) + b => b = 0.42 

y = 3.14x + 0.42 



Diameter = 12 inches 
Diameter = 25 inches 
Diameter = 60 inches 



y = 3.14(12) + 0.42 = 38.1 inches 
y = 3.14(25) + 0.42 = 78.92 inches 
y = 3.14(60) + 0.42 = 188.82 inches 



In this problem, the slope = 3.14. This number should be very familiar to you — it is the number pi rounded 
to the hundredths place. Theoretically, the circumference of a circle divided by its diameter is always the 
same and it equals 3.14 or n. 

Example 2: A cylinder is filled with water to a height of 73 centimeters. The water is drained through 
a hole in the bottom of the cylinder and measurements are taken at two-second intervals. The table below 
shows the height of the water level in the cylinder at different times. 

Find the water level at 15 seconds. 

Solution: Begin by graphing the scatter plot. As you can see below, a straight line does not fit the majority 
of this data. Therefore, there is no line of best fit. Instead, use interpolation. 

Table 5.11: Water Level in Cylinder at Various Times 



Time (seconds) 



Water level (cm) 



0.0 
2.0 
4.0 
6.0 
8.0 
10.0 



73 

63.9 

55.5 

47.2 

40.0 

33.4 



www.ckl2.org 



208 



Table 5.11: (continued) 



Time (seconds) 



Water level (cm) 



12.0 
14.0 
16.0 
18.0 
20.0 
22.0 
24.0 
26.0 
28.0 
30.0 



27.4 

21.9 

17.1 

12.9 

9.4 

6.3 

3.9 

2.0 

0.7 

0.1 



Time vs. Water Level of Cylinder 




10 15 20 25 
Time (seconds) 

Time vs. Water Level of Cylinder 



.Q> 

3: 



y, 

100 
80 
60 
40 h 
20 



-5 



h 














t 














• 














• 


• 














< 


• 


f = 15 














• 




t = 2 


7x 



10 15 20 
Time (seconds) 



209 



www.ckl2.org 



To find the value at 15 seconds, connect points (14, 21.9) and (16, 17.1) and find the equation of the 
straight line. 



17.1-21.9 -4.8 

m = = = -2.4 

16-14 2 



y = -2 Ax + Z? => 21.9 = -2.4(14) + b => b = 55.5 



Equation y = -2 Ax + 55.5 

Substitute x = 15 and obtain y = -2.4(15) + 55.5 = 19.5 cm. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Using a Linear Model (12:14) 




Figure 5.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/765 



1. What is a mathematical model? 

2. What is linear modeling^ What are the options to determine a linear model? 

3. Using the Water Level data, use interpolation to determine the height of the water at 17 seconds. 

Use the Life Expectancy table below to answer the questions. 

4. Make a scatter plot of the data. 

5. Use a line of best fit to estimate the life expectancy of a person born in 1955. 

6. Use linear interpolation to estimate the life expectancy of a person born in 1955. 

7. Use a line of best fit to estimate the life expectancy of a person born in 1976. 

8. Use linear interpolation to estimate the life expectancy of a person born in 1976. 

9. Use a line of best fit to estimate the life expectancy of a person born in 2012. 

10. Use linear extrapolation to estimate the life expectancy of a person born in 2012. 

11. Which method gives better estimates for this data set? Why? 



www.ckl2.org 



210 



Table 5.12: 



Birth Year Life expectancy in years 

1930 59.7 

1940 62.9 

1950 68.2 

1960 69.7 

1970 70.8 

1980 73.7 

1990 75.4 

2000 77 



The table below lists the high temperature for the first day of each month in 2006 in San Diego, California 
(Weather Underground). Use this table to answer the questions. 

12. Draw a scatter plot of the data. 

13. Use a line of best fit to estimate the temperature in the middle of the 4 th month (month 4.5). 

14. Use linear interpolation to estimate the temperature in the middle of the 4 th month (month 4.5). 

15. Use a line of best fit to estimate the temperature for month 13 (January 2007). 

16. Use linear extrapolation to estimate the temperature for month 13 (January 2007). 

17. Which method gives better estimates for this data set? Why? 

Table 5.13: 

Month number Temperature (F) 

1 63 

2 66 

3 61 

4 64 

5 71 

6 78 

7 88 

8 78 

9 81 

10 75 

11 68 

12 69 



Mixed Review 

18. Simplify 6f(-2 + It) - r(4 + St). 

19. Solve for y : ^ = =f- (y + \) - \. 

20. Determine the final cost. Original cost of jacket: $45.00; 15% percent markup; and 8% sales tax. 

21. Write as a fraction: 0.096. 

22. Is this function an example of direct variation? g(t) = —35t+ 15. Explain your answer. 

23. The following data shows the number of youth-aged homicides at school during various years (source: 
http : //nces . ed . gov/programs/crimeindicators/crimeindicators2009/tables/table_01_l . asp) 



211 www.ckl2.org 



Year 


1993 


1995 


1997 


1999 


2001 


2003 


2005 


2007 


# 


34 


28 


28 


33 


14 


18 


22 


30 



(a) Graph this data and connect the data points. 

(b) What conclusions can you make regarding this data? 

(c) There seems to be a large drop in school homicides between 1999 and 2001. What could have 
happened to cause such a large gap? 

(d) Make a prediction about 2009 using this data. 

5.8 Problem- Solving Strategies: Dimensional Anal- 
ysis 

Real- world information is given in dimensions, or the units in which the value is measured. For example, 
the following are all examples of dimensions. 

Inches 

Feet 

Liters 

Micrograms 

Acres 

Hours 

Pounds 

Students 

Analyzing dimensions can help you solve problems in travel, astronomy, physics, engineering, forensics, 
and quality. Solving problems by converting dimensions or canceling dimensions is the focus of this lesson. 



!lll,iiiiiffi |li,r ! ' 



^mmu^ii^ 



i "I'MIIHHHHI •■"! 

-1mm 4 








Consider the distance formula distance = rate • time. This formula can be rewritten for rate, rate = dlstance . 

time 

If distance is measured in kilometers, and time is measured in hours, the rate would have the dimensions 

kilometers 
hours 

You can treat dimensions as variables. Identical units can divide out, or cancel. For example, kll °l^ e ^ rs * 
hour -> Miners .h^rf^ kilometers. 

hoar 

Sometimes the units will not divide out. In this case, a conversion factor is needed. 
Example: Convert 35 k %™ ters to meters. 



www.ckl2.org 212 



Solution: Since kilometers ± meters, you need to convert kilometers to meters to get the answer. You 
know there are 1,000 meters in a kilometer. Therefore, you will need to multiply the original dimension 
by this factor. 

35 kilometers 1000 meters 35 kilometers 1000 meters 

• — — • hour — > • — — — — • never ' — 35 ( 1000 )meters. 

hour 1 kilometer hour 1 kuemeter 

35 kilometers 

= 35, 000 meters 

hour 

The process of using units or dimensions to help solve a problem is called dimensional analysis. It is 
very useful in chemistry and travel, as shown in the examples below. 

Example: How many seconds are in a month? 

Solution: This situation can be solved easily using multiplication. However, the process you use when 
multiplying the values together is an example of dimensional analysis. 

Begin with what you know: 

• 60 seconds in one minute 

• 60 minutes in one hour 

• 24 hours in one day 

• Approximately 30 days in one month 







r 



y 



Now write the expression to convert the seconds in one minute to one month. 

60 seconds 60 minutes 24 hours 30 days 
1 minute 1 hour 1 day 1 month 

Identical units cross-cancel. 

60 seconds 60 rnirmtes 24 hetefs 30 djxfs 



1 rmntffe 1 hoxrf 1 (lerf 1 month 



Multiply the fractions together. 

60 • 60 • 24 • 30 seconds seconds 

1 • 1 • 1 • 1 month ' month 

Example 1: How many grams are in 5 pounds? 

Solution: Begin by writing all the conversions you know related to this situation. 



213 www.ckl2.org 



1 gram « 0.0353 ounces 
16 ounces = 1 pound 

Write your dimensional analysis. 

16 ounces 1 gram 



5 pounds 



1 pound 0.0353 ounce 

Cross-cancel identical units and multiply. 

16 .ameer 1 gram 

5 pounds- — • — = 2226.29 grams 

1 pmma 0.0353 Qimcg 

A long list of conversion factors can be found at this website . 

Practice Set 

1. True or false? Dimensional analysis is the study of space and time. 

2. By using dimensional analysis, what happens to identical units that appear diagonally in the multi- 
plication of fractions? 

3. How many feet are in a mile? 

4. How many inches are in a mile? 

5. How many seconds are in a day? 

6. How many seconds are in a year? 

7. How many feet are in a furlong? 

8. How many inches are in 100 yards (one football field)? 

9. How many centimeters are in 5 inches? 

10. How many meters are between first and second base (90 feet)? 

11. How many meters are in 16 yards? 

12. How many cups are in 6 liters? 

13. How many cubic inches make up one ounce? 

14. How many milliliters make up 8 ounces? 

15. How many grams are in 100 pounds? 

16. An allergy pill contains 25 mg of Diphenhydramine. If 1 gram = 15.432 grains, how many grains of 
this medication is in the allergy pill? 

17. A healthy individual's heart beats about 68 times per minute. How many beats per hour is this? 

18. You live 6.2 miles from the grocery store. How many fathoms is this? (6 feet = 1 fathom) 

19. The cost of gas in England is 96.4 pound sterling /liter. How much is this in U.S. dollars/gallon'? 
(3.875 litres = 1 gallon and 1.47 US $ = 1 pound sterling) 

20. Light travels 186 f e ° c ° on ™ iles • How long is one light year? 

21. Another way to describe light years is in astronomical units. If 1 light year = 63, 240 AU (astronomical 
units), how far in AUs is Alpha Centauri, which is 4.32 light years from the Earth? 

22. How many square feet is 16 acres? 

23. A person weighs 264 pounds. How many kilograms is this weight? 

24. A car is traveling 65 miles/hour and crosses into Canada. What is this speed in km/hr? 

25. A large soda cup holds 32 ounces. What is this capacity in cubic inches? 

26. A space shuttle travels 28,000 mph. What is this distance in feet/second! 

27. How many hours are in a fortnight (two weeks)? 

www.ckl2.org 214 



28. How many fortnights (two- week periods) are in 2 years? 

29. A semi truck weighs 32,000 pounds empty. How many tons is this weight? 

30. Which has the greatest volume: a 2-liter bottle of soda, one gallon of water, or 10 pints of human 
blood? 

Mixed Review 

31. Solve for x : -2x + 8 = 8(1 - 4x). 

32. Simplify: 3 - 2(5 - 8/z) + 13/z • 3. 

33. Find the difference: -26.375 - (-14|). 

34. Find the product: -2f • ^. 

35. Simplify: V80. 

36. Is 5.5 an irrational number? Explain your answer. 

Use the relation given for the following questions: {(0, 8), (1, 4), (2, 2), (3, 1), (4, ^) , (5, |)}. 

37. State the domain. 

38. State the range. 

39. Is this relation a function? Explain your answer. 

40. What seems to be the pattern in this relation? 

5.9 Chapter 5 Review 

Find an equation of the line in slope-intercept form using the given information. 

1. (3, 4) with slope = | 

2. slope = -5, y - intercept = 9 

3. slope = -1 containing (6, 0) 

4. containing (3.5, 1) and (9, 6) 

5. slope = 3, y- intercept = -1 

6. slope = ^ containing (-3, -4) 

7. containing (0, 0) and (9, -8) 

8. slope = |, y- intercept = 6 

9. containing (5, 2) and (-6, -3) 

10. slope = 3 and /(6) = 1 

11. /(2) = -5 and /(-6) = 3 

12. slope = | and /(l) = 1 

Find an equation of the line in point-slope form using the given information. 

13. slope = m containing (xi,yi) 

14. slope = \ containing (-7, 5) 

15. slope = 2 containing (7, 0) 

Graph the following equations. 

16. y + 3 = -(jc-2) 

215 www.ckl2.org 



17. y -7 = =f(x + 5) 

18. y + 1.5 = |(jc + 4) 

Find the equation of the line represented by the function below in point-slope form. 

19. /(I) = -3 and /(6) = 

20. /(9) = 2 and /(9) = -5 

21. /(2) = and slope = § 

Write the standard form of the equation of each line. 

23. y- 3 = ^(x + 4) 

24. y = f(x-21) 

25. -3;t-25 = 5y 

Write the standard form of the line for each equation using the given information. 

25. containing (0, -4) and (-1, 5) 

26. slope = | containing (3, 2) 

27. slope = 5 containing (5, 0) 

28. Find the slope and y-intercept of 7x + 5y = 16. 

29. Find the slope and y-intercept of 7x - 7y = -14. 

30. Are \x + \y = 5 and 2x + 2y = 3 parallel, perpendicular, or neither? 

31. Are x = 4 and y = -2 parallel, perpendicular, or neither? 

32. Are 2x + 8y = 26 and x + 4y = 13 parallel, perpendicular, or neither? 

33. Write an equation for the line perpendicular to y = 3x + 4 containing (-5, 1). 

34. Write an equation for the line parallel to y = x + 5 containing (-4, -4). 

35. Write an equation for the line perpendicular to 9x + 5y = 25 containing (-4, 4). 

36. Write an equation for the line parallel to y = 5 containing (-7, 16). 

37. Write an equation for the line parallel to x = containing (4, 6). 

38. Write an equation for the line perpendicular to y = -2 containing (10, 10). 

39. An Internet cafe charges $6.00 to use 65 minutes of their Wifi. It charges $8.25 to use 100 minutes. 
Suppose the relationship is linear. 

(a) Write an equation to model this data in point-slope form. 

(b) What is the price to acquire the IP address? 

(c) How much does the cafe charge per minute? 

40. A tomato plant grows \ inch per week. The plant was 5 inches tall when planted. 

(a) Write an equation in slope-intercept form to represent this situation. 

(b) How many weeks will it take the plant to reach 18 inches tall? 

41. Joshua bought a television and paid 6% sales tax. He then bought an albino snake and paid 4.5% 
sales tax. His combined purchases totaled $679.25. 

(a) Write an equation to represent Joshua's purchases. 

(b) Graph all the possible solutions to this situation. 

(c) Give three examples that would be solutions to this equation. 

42. Comfy Horse Restaurant began with a 5-gallon bucket of dishwashing detergent. Each day \ gallon 
is used. 

(a) Write an equation to represent this situation in slope-intercept form. 
www.ckl2.org 216 



2001 


2002 


2003 


2004 


2005 


2006 


2007 


5.8 


5.4 


5.4 


5.3 


5.4 


5.3 


5.0 



(b) How long will it take to empty the bucket? 

43. The data below shows the divorce rate per 1,000 people in the state of Wyoming for various years 
(source: Nation Masters ). 

(a) Graph the data in a scatter plot. 

(b) Fit a line to the data by hand. 

(c) Find the line of best fit by hand. 

(d) Using your model, what do you predict the divorce rate is in the state of Wyoming in the year 
2011? 

(e) Repeat this process using your graphing calculator. How close was your line to the one the 
calculator provided? 

Year 2000 

Rate (per 1,000 people) 5.8 

44. The table below shows the percentage of voter turnout at presidential elections for various years 
(source The American Presidency Project ). 

Year 1828 1844 1884 1908 1932 1956 1972 1988 2004 

% of Voter Turnout 57.6 78.9 77.5 65.4 56.9 60.6 55.21 50.15 55.27 

(a) Draw a scatter plot of this data. 

(b) Use the linear regression feature on your calculator to determine a line of best fit and draw it on your 
graph. 

(c) Use the line of best fit to predict the voter turnout for the 2008 election. 

(d) What are some outliers to this data? What could be a cause for these outliers? 

45. The data below shows the bacteria population in a Petri dish after h hours. 



h hours 





1 


2 


3 


4 


5 


6 


Bacteria present 


100 


200 


400 


800 


1600 


3200 


6400 



(a) Use the method of interpolation to find the number of bacteria present after 4.25 hours. 

(b) Use the method of extrapolation to find the number of bacteria present after 10 hours. 

(c) Could this data be best modeled with a linear equation? Explain your answer. 

46. How many seconds are in 3 months? 

47. How many inches are in a kilometer? 

48. How many cubic inches are in a gallon of milk? 

49. How many meters are in 100 acres? 

50. How many fathoms is 616 feet? 



5.10 Chapter 5 Test 



1. Write y = -^-x + 4 in standard form. 



2. Write an equation in slope-intercept form for a line perpendicular to y = ~x + 6 containing (1, 2). 

3. Write an equation in point-slope form for a line containing (5, 3) and (-6, 0.5). 

217 www.ckl2.org 



4. What is the speed of a car travelling 80 miles/hour in feet/second? 

5. How many kilometers are in a marathon (26.2 miles)? 

6. Lucas bought a 5-gallon container of paint. He plans to use § gallon per room. 

(a) Write an equation to represent this situation. 

(b) How many rooms can Lucas paint before the container is empty? 

7. Are these two lines parallel, perpendicular, or neither? Explain your answer by showing your work: 
y = 3x - 1 and -x + 3y = 6. 

8. The table below gives the gross public debt of the U.S. Treasury for the years 2004-2007. 

Year 2004 2005 2006 2007 

Debt (in billions $) 7, 596.1 8, 170.4 8, 680.2 9, 229.2 

(a) Make a scatter plot of the data. 

(b) Use the method of extrapolation to determine the gross public debt for 2009. 

(c) Find a linear regression line using a graphing calculator. 

(d) Use the equation found in (c) to determine the gross public debt for 2009. 

(e) Which answer seems more accurate, the linear model or the extrapolation? 

9. What is the process used to interpolate data? 

10. Use the table below to answer the following questions. 

Hours (h) 12 3 4 

Percentage of mineral remaining 100 50 25 12.5 6.25 

(a) Draw a scatter plot to represent the data. 

(b) Would a linear regression line be the best way to represent the data? 

(c) Use the method of interpolation to find the percentage of mineral remaining when h = 2.75. 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/flexr/chapter/9615. 



www.ckl2.org 218 



Chapter 6 

Linear Inequalities and 
Absolute Value; An 
Introduction to Probability 



This chapter moves beyond equations to the study of inequalities. Many situations have more than one 
correct answer. A police officer can issue a ticket for any speed exceeding the limit. A rider for the bumper 
boats must be less than 48 inches tall. Both these situations have many possible answers. 




6.1 Inequalities Using Addition and Subtraction 

Verbs that translate into inequalities are: 

> "greater than" 

> "greater than or equal to" 

< "less than" 

< "less than or equal to" 

=£ "not equal to" 

Definition: An algebraic inequality is a mathematical sentence connecting an expression to a value, a 
variable, or another expression with an inequality sign. 

Solutions to one-variable inequalities can be graphed on a number line or in a coordinate plane. 

Example: Graph the solutions to t > 3 on a number line. 

219 www.ckl2.org 



Solution: The inequality is asking for all real numbers larger than 3. 

<«— I — I 1 — I 1 1 1 — I — I — I — I 1 — I — O — I — I — I — I — I — I — !-► 

-10 -9-8-7-6-5-4-3-2-1 1 2 3 4 5 6 7 8 9 10 

You can also write inequalities given a number line of solutions. 
Example: Write the inequality pictured below. 

<«— I — I — I — I — I — I — I — I — I — I — I — I — I — I # I 1 — I 1 — I !-► 

-10 -9-8-7-6-5-4-3-2-10 1 2 3 4 5 6 7 8 9 10 

Solution: The value of four is colored in, meaning that four is a solution to the inequality. The red arrow 
indicates values less than four. Therefore, the inequality is: 

x < 4 

Inequalities that "include" the value are shown as < or >. The line underneath the inequality stands for 
"or equal to." We show this relationship by coloring in the circle above this value on the number line, as in 
the previous example. For inequalities without the "or equal to," the circle above the value on the number 
line remains unfilled. 

Four Ways to Express Solutions to Inequalities 

1. Inequality notation: The answer is expressed as an algebraic inequality, such as d < \. 

2. Set notation: The inequality is rewritten using set notation brackets { }. For example, \d\d < ^} is read, 
"The set of all values of d, such that d is a real number less than or equal to one-half." 

3. Interval notation: This notation uses brackets to denote the range of values in an inequality. 

1. Square or "closed" brackets [ ] indicate that the number is included in the solution 

2. Round or "open" brackets ( ) indicate that the number is not included in the solution. 

Interval notation also uses the concept of infinity oo and negative infinity -oo. For example, for all values 
of d that are less than or equal to |, you could use set notation as follows: (-oo, i|. 

4. As a graphed sentence on a number line. 

Example: (8, 24) states that the solution is all numbers between 8 and 24 but does not include the 
numbers 8 and 24. 

[3, 12) states that the solution is all numbers between 3 and 12, including 3 but not including 12. 

Inequalities Using Addition or Subtraction 

To solve inequalities, you need some properties. 

Addition Property of Inequality: For all real numbers a, b, and c: 

If x < a, then x + b < a + b. 

If x < a, then x- c < a - c. 

The two properties above are also true for < or >. 

www.ckl2.org 220 



Because subtraction can also be thought of as "add the opposite," these properties also work for sub- 
traction situations. 

Just like one-step equations, the goal is to isolate the variable, meaning to get the variable alone on one 
side of the inequality symbol. To do this, you will cancel the operations using inverses. 

Example: Solve for x : x - 3 < 10. 

Solution: To isolate the variable x, you must cancel "subtract 3" using its inverse operation, addition. 

x-3 + 3<10 + 3 
x< 13 

Now, check your answer. Choose a number less than 13 and substitute it into your original inequality. If 
you choose 0, and substitute it you get: 

0-3 < 10 = -3< 10 

What happens at 13? What happens with numbers greater than 13? 

Example: Solve for x : x + 4 > 13 

Solution: 

To solve the inequality x + 4 > 13 

Subtract 4 from both sides of the inequality. x + 4-4>13-4 

Simplify. x > 9 

<«— I — I 1 — I I I 1 1 — I — I — I I — I — I — O — I — I — I — I — I — !-► 

-5-4-3-2-10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

Writing Real-Life Inequalities 

As described in the chapter opener, inequalities appear frequently in real life. Solving inequalities is an 
important part of algebra. 

Example: Write the following statement as an algebraic inequality. You must maintain a balance of at 
least $2,500 in your checking account to avoid a finance charge. 

Solution: The key phrase in this statement is "at least." This means you can have $2,500 or more in your 
account to avoid a finance charge. 

Choose the variable to describe the money in your account, say m. 

Write the inequality: m > 2500. 

Graph the solutions using a number line. 

<— I 1 1 1 1 1 1 1 1 1 1 1 1 — I • I 1 1 1 1 !-► 

-1000 -500 500 1000 1500 2000 2500 3000 3500 4000 

Example: Translate into an algebraic inequality: "The speed limit is 65 miles per hour." 

Solution: To avoid a ticket, you must drive 65 or less. Choose a variable to describe your possible speed, 
say s. 

11\ www.ckl2.org 



Write the inequality s < 65. 

Graph the solutions to the inequality using a number line. 

^— I — I — I — I — I — I — I — I — I — I — I 1 — I — I 1 — I — !-•+ 



^ — i — !-► 



-100-90-80-70-60-50-40-30-20-10 10 20 30 40 50 60 70 80 90 100 

In theory, you cannot drive a negative number of miles per hour. This concept will be a focus later in this 
chapter. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Inequalities Using Addition and Subtraction (7:48) 




Figure 6.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/766 



1. What are the four methods of writing the solution to an inequality? 
Graph the solutions to the following inequalities using a number line. 

2. x< -3 

3. x> 6 

4. x>0 

5. x<8 

6. x < -35 

7. x>-Yl 

8. x > 20 

9. x<3 

Write the inequality that is represented by each graph. 

10 - <— I — I — I — I — I — I • I — I — I — I — I — I — I 1 — I — I — I — I — I — !-► 

-18-17-16-15-14-13-12-11-10-9 -8 -7-6-5-4 -3 -2-10 1 2 

n - <«— I — I 1 1 1 1 1 1 1 1 — I 1 — I — I — I — \Ch-\ — I — I — I — !-► 

-1000 -800 -600 -400 -200 200 400 600 800 1000 



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222 



12 <— I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — HH — I — I — !-► 
-10 -9-8-7-6-5-4-3-2-10 1 2 3 4 5 6 7 8 9 10 

13 - <— I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — l-»H — !-► 
-100 -90-80-70-60-50-40-30-20-10 10 20 30 40 50 60 70 80 90 100 

14 - <— I — I — I — I — I — I — I — I — I — I — I — I — I — O — I — I — I — I — I — I — !-► 
-100-90-80-70-60-50-40-30-20-10 10 20 30 40 50 60 70 80 90 100 

15 <— I — I — I — I — I — I — I — I — I — I • I — I — I — I — I — I — I — I — I — !-► 

-20-19-18-17-16-15-14-13-12-11-10-9 -8 -7 -6 -5 -4 -3 -2 -1 

16 «*— I — I — I — I — I — I — I — l—O — I — I — I — I — I — I — I — I — I — I — I — !-► 

-50^5^10-35-30-25-20-15-10-5 5 10 15 20 25 30 35 40 45 50 

17 ««— I — I — I — I — I — I — I — I — I — I — I • I — I — I — I — I — I — I — I — !-► 

-10 -9-8-7-6-5-4-3-2-1 1 2 3 4 5 6 7 8 9 10 

Write the inequality given by the statement. Choose an appropriate letter to describe the unknown 
quantity 

18. You must be at least 48 inches tall to ride the "Thunderbolt" Rollercoaster. 

19. You must be younger than 3 years old to get free admission at the San Diego Zoo. 

20. Charlie needs more than $1,800 to purchase a car. 

21. Cheryl can have no more than six pets at her house. 

22. The shelter can house no more than 16 rabbits. 

Solve each inequality and graph the solution on the number line. 

23. x-l> -10 

24. x - 1 < -5 

25. -20 + a> 14 

26. x + 2<7 

27. x + 8<-7 

28. 5 + /> | 

29. x-5<35 

30. 15 + g>-60 

31. x-2< 1 

32. x-8> -20 

33. ll + <z> 13 

34. x + 65 < 100 

35. x-32<0 

36. x + 68 > 75 

37. 16 + y<0 

Mixed Review 

38. Write an equation containing (3, -6) and (-2, -2). 

39. Simplify: |2 - 11 X 3| + 1. 

40. Graph y = — 5 on a coordinate plane. 

223 www.ckl2.org 



41. y varies directly as x. When x = — 1, y = g. Find y when x = -4*. 

42. Rewrite in slope-intercept form: -2x. 

43. -2x + 7y = 63 

6.2 Inequalities Using Multiplication and Divi- 
sion 

Equations are mathematical sentences in which the two sides have the same "weight." By adding, sub- 
tracting, multiplying, or dividing the same value to both sides of the equation, the balance stays in check. 
However, inequalities begin off-balance. When you perform inverse operations, the inequality will remain 
off-balance. This is true with inequalities involving both multiplication and division. 

Before we can begin to solve inequalities involving multiplication or division, you need to know two prop- 
erties, the Multiplication Property of Inequalities and the Division Property of Inequalities. 

Multiplication Property of Inequality: For all real positive numbers a, b, and c: 

If x < a, then x(c) < a(c). 

If x > a, then x(c) > a(c). 

Division Property of Inequality: For all real positive numbers a, b, and c: 

If x < a, then x -f (c) < a -f (c). 

If x > a, then x-r (c) > a-r (c). 

Consider the inequality 2x > 12. To find the solutions to this inequality, we must isolate the variable x by 
using the inverse operation of "multiply by 2," which is dividing by 2. 

2x> 12 

2x 12 

~2~ " ~2~ 

x> 6 

This solution can be expressed in four ways. One way is already written, x > 6. Below are the three 
remaining ways to express this solution: 

• {x\x>6} 

• [6,oo) 

• Using a number line: 

*4— I — I — I — I — I — I — I — I — I — I — I 1 — I — I 1 — I • I — I — I — !-► 

-10 -9-8-7-6-5-4-3-2-10 1 2 3 4 5 6 7 8 9 10 

Example: Solve for y : | < 3. Express the solution using all four methods. 

Solution: The inequality above is read, "y divided by 5 is less than or equal to 3." To isolate the variable 
y, you must cancel division using its inverse operation, multiplication. 

y 5 5 

-• - <3- - 
5 1 1 

y< 15 
www.ckl2.org 224 



One method of writing the solution is y < 15. 
The other three are: 

• (-oo,15] 

• {y\y< 15} 

• <— I — I — I — I — I — I — I — I 1 — I — I 1 — I— O—l — I — I — I — I — I !-► 

-50^5^10-35 -30 -25-20-15 -10 -5 5 10 15 20 25 30 35 40 45 50 

Multiplying and Dividing an Inequality by a Negative Number 

Notice that the two properties in this lesson focused on c being only positive. This is because those 
particular properties of multiplication and division do not apply when the number being multiplied (or 
divided) is negative. 

Think of it this way. When you multiply a value by -1, the number you get is the negative of the original. 

6(-l) = -6 

Multiplying each side of a sentence by -1 results in the opposite of both values. 

5jc(-1) = 4(-l) 
-5x = -4 

When multiplying by a negative, you are doing the "opposite" of everything in the sentence, including the 
verb. 

x > 4 

*(-!)> 4(-l) 

-x < -4 

This concept is summarized below. 

Multiplication/Division Rule of Inequality: For any real number a, and any negative number c, 

If x < a, then x • c > a • c 

If x < a, then - > - 

J ' c c 

As with the other properties of inequalities, these also hold true for < or >. 

Example 1: Solve for r : -3r < 9. 

Solution: To isolate the variable r, we must cancel "multiply by -3" using its inverse operation, dividing 
by -3. 

-3r 9 
^3~ < ^3 

Since you are dividing by -3, everything becomes opposite, including the inequality sign. 

r>-3 
Example 2: Solve for p : I2p < -30. 

225 www.ckl2.org 



Solution: To isolate the variable p 1 we must cancel "multiply by 12" using its inverse operation, dividing 
by 12. 

12/7 -30 

U < T2" 

Because 12 is not negative, you do not switch the inequality sign. 

-5 

P < — 
F 2 

In set notation, the solution would be: f-00, ^J 

Multimedia Link: For more help with solving inequalities involving multiplication and division, visit 
Khan Academy's website: http://khanexercises .appspot . com/video?v=PNXozoJWsWc. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Inequalities Using Multiplication and Division (10:27) 



Video 



Figure 6.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/767 



1. In which cases do you change the inequality sign? 
Solve each inequality. Give the solution using inequality notation and with a solution graph. 



2. 3x < 6 

°' 5 > 10 

4. -10* > 250 

5. Af > -5 

6. 9x> -| 
7- zf5<5 

8. 620x > 2400 

9 — > - — 

Vm 20 - 40 

10. -0.5jc < 7.5 

11. 75jc> 125 



www.ckl2.org 



226 



12. 4>-f 

13. zfj < 1 

14. ^fg < 8 

15. § > 40 

16. ^ < -12 
17 — < - 

- 1 '- 25 ^ 2 

18. Af > 9 

19. 4* < 24 

20. 238 < Ud 

21. -19m < -285 

22. -9x>-§ 

23. -5jc < 21 

24. The width of a rectangle is 16 inches. Its area is greater than 180 square inches. 

(a) Write an inequality to represent this situation. 

(b) Graph the possible lengths of the rectangle. 

25. Ninety percent of some number is at most 45. 

(a) Write an inequality to represent the situation. 

(b) Write the solutions as an algebraic sentence. 

26. Doubling Martha's jam recipe yields at least 22 pints. 

(a) Write an inequality to represent the situation. 

(b) Write the solutions using interval notation. 

Mixed Review 

27. After 3 dozen cookies, Anna has fewer than 24 to make. 

(a) Write an inequality to represent this situation. Let c = the number of cookies Anna had to 
make. 

(b) Write the solutions in set notation. 

28. Tracey's checking account balance is $31.85. He needs to deposit enough money to pay his satellite 
T.V. bill, which is $97.12. 

(a) Write an inequality to represent this situation. 

(b) Write the solutions as an algebraic sentence. 

29. Solve for v : v = -|2 - (-19) + 6|. 

30. A piggy bank is filled with dimes and quarters. The total amount of money is $26.00. 

(a) Graph all the combinations that make this statement true. 

(b) If $13.50 is in quarters, how many dimes must be in the piggy bank? 



6.3 Multi-Step Inequalities 



The previous two lessons focused on one-step inequalities. Inequalities, like equations, can require several 
steps to isolate the variable. These inequalities are called multi-step inequalities. With the exception of 
the Multiplication/Division Property of Inequality, the process of solving multi-step inequalities is identical 
to solving multi-step equations. 

Procedure to Solve an Inequality: 

227 www.ckl2.org 



1. Remove any parentheses by using the Distributive Property. 

2. Simplify each side of the inequality by combining like terms. 

3. Isolate the ax term. Use the Addition/Subtraction Property of Inequality to get the variable on one 
side of the inequality sign and the numerical values on the other. 

4. Isolate the variable. Use the Multiplication/Division Property of Inequality to get the variable alone 
on one side of the inequality. 

(a) Remember to reverse the inequality sign if you are multiplying or dividing by a negative number. 

5. Check your solution. 

Example: Solve for w : 6x - 5 < 10. 
Solution: Begin by using the checklist above. 

1. Parentheses? No 

2. Like terms on the same side of inequality? No 

3. Isolate the ax term using the Addition Property. 

6jc-5 + 5<10 + 5 

Simplify. 

6x< 15 

4. Isolate the variable using the Multiplication or Division Property. 

6x 15 5 

— < — = x < - 

6 6 2 

5. Check your solution. Choose a number less than 2.5, say 0, and check using the original inequality. 

6(0) -5 < 10? 
-5< 10 

Yes, the answer checks, x < 2.5 
Example: Solve for x : -9x < -5x - 15 
Solution: Begin by using the checklist above. 

1. Parentheses? No 

2. Like terms on the same side of inequality? No 

3. Isolate the ax term using the Addition Property. 

-9x + 5x < -5x + 5x - 15 

Simplify. 

-4jc < -15 

4. Isolate the variable using the Multiplication or Division Property. 
www.ckl2.org 228 



-4* -15 
< 

-4 -4 

Because the number you are dividing by is negative, you must reverse the inequality sign. 

15 3 

x > — > x > 3- 

4 4 

5. Check your solution by choosing a number larger than 3.75, say 10. 

-9(10) < -5(10) -15? 
/ - 90 < -65 

Example: Solve for x : 4x - 2(3jk - 9) < -4(2jk - 9). 
Solution: Begin by using the previous checklist. 

1. Parentheses? Yes. Use the Distributive Property to clear the parentheses. 

4x+ (-2)(3jc) + (-2) (-9) < -4(2*) + (-4)(-9) 
Simplify. 

4x - 6x + 18 < -8x + 36 

2. Like terms on the same side of inequality? Yes. Combine these. 

-2jc+ 18 < -8x + 36 

3. Isolate the ax term using the Addition Property. 

-2x + 8x + 18 < -8jc + 8x + 36 

Simplify. 

6x + 18 < 36 
6x+18-18<36-18 
6x< 18 

4. Isolate the variable using the Multiplication or Division Property. 

6x 18 

— < — ^ x<3 
6 6 

5. Check your solution by choosing a number less than 3, say -5. 

4(-5) - 2(3 • -5 - 9) < -4(2 • -5 - 9) 
y 28 < 76 

229 www.ckl2.org 



Identifying the Number of Solutions to an Inequality 

Inequalities can have infinitely many solutions, no solutions, or a finite set of solutions. Most of the 
inequalities you have solved to this point have an infinite amount of solutions. By solving inequalities and 
using the context of a problem, you can determine the number of solutions an inequality may have. 

Example: Find the solutions to x - 5 > x + 6. 

Solution: Begin by isolating the variable using the Addition Property of Inequality. 

x-x-5>x-x-\-6 

Simplify. 

-5>6 

This is an untrue inequality. Negative five is never greater than six. Therefore, the inequality x— 5 > x-\- 6 
has no solutions. 

Previously we looked at the following sentence: "The speed limit is 65 miles per hour." 

The algebraic sentence for this situation is: s < 65. 

Example: Find the solutions to s < 65. 

Solution: The speed at which you drive cannot be negative. Therefore, the set of possibilities using 
interval notation is [0, 65]. 

Solving Real- World Inequalities 

Example: In order to get a bonus this month, Leon must sell at least 120 newspaper subscriptions. He 
sold 85 subscriptions in the first three weeks of the month. How many subscriptions must Leon sell in the 
last week of the month? 

Solution: The amount of subscriptions Leon needs is "at least" 120. Choose a variable to represent 
the varying quantity-the number of subscriptions, say n. The inequality that represents the situation is 
rc + 85> 120. 

Solve by isolating the variable n: n > 35. 

Leon must sell 35 or more subscriptions to receive his bonus. 

Example: The width of a rectangle is 12 inches. What must the length be if the perimeter is at least 180 
inches? (Note: Diagram not drawn to scale.) 



12 in 



12 in 



x 

Solution: The perimeter is the sum of all the sides. 

12 + 12 + x + x> 180 

www.ckl2.org 230 



Simplify and solve for the variable x: 



12 + 12 + x + x> 180 
2x > 156 

x>78 



24 + 2x > 180 



The length of the rectangle must be 78 inches or larger. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Multi-Step Inequalities (8:02) 




Figure 6.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/768 

In 1 - 15, solve each of the inequalities and graph the solution set. 



1. 


6x - 5 < 10 


2. 


-9x < -5x - 15 


3. 


-^ <24 


4. 


f -7>-3x+12 


5. 


5fi>-2(x + 5) 



6. 4x + 3<-l 

7. 2x<7x-36 

8. 5x > 8x + 27 

9. 5-x<9 + x 

10. 4-6x<2(2x + 3) 

11. 5(4x + 3) >9(x-2)-x 

12. 2(2x-l) + 3<5(x + 3)-2x 

13. 8x - 5(4x + 1) > -1 + 2(4x - 3) 

14. 2(7x - 2) - 3(x + 2) < 4x - (3x + 4) 

15. |x-i(4x-l) >x + 2(x-3) 

16. At the San Diego Zoo, you can either pay $22.75 for the entrance fee or $71 for the yearly pass, which 
entitles you to unlimited admission. At most, how many times can you enter the zoo for the $22.75 
entrance fee before spending more than the cost of a yearly membership? 

17. Proteek's scores for four tests were 82, 95, 86, and 88. What will he have to score on his last test to 
average at least 90 for the term? 



231 



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18. Raul is buying ties and he wants to spend $200 or less on his purchase. The ties he likes the best 
cost $50. How many ties could he purchase? 

19. Virena's Scout Troop is trying to raise at least $650 this spring. How many boxes of cookies must 
they sell at $4.50 per box in order to reach their goal? 

Mixed Review 

20. Solve: 10 > -5/. 

21. Graph y = -7 on a coordinate plane. 

22. Classify V5 using the real number hierarchy. 

23. What are some problem-solving methods you have learned so far in this textbook? List one example 
for each method. 

24. A circle has an area of A = 7ir 2 . What is the radius of a circle with area of 1967T in 2 ? 

25. Solve for a : f = ^g. 



6.4 Compound Inequalities 



Inequalities that relate to the same topic can be written as a compound inequality. A compound 
inequality involves the connecting words "and" and "or." 

The word and in mathematics means the intersection between the sets. 

"What the sets have in common." 

The word or in mathematics means the union of the sets. 

"Combining both sets into one large set." 

Inequalities Involving "And" 

Consider, for example, the speed limit situation from the previous lesson. Using interval notation, the 
solutions to this situation can be written as [0, 65]. As an inequality, what is being said it this: 

The speed must be at least mph and at most 65 mph. 

Using inequalities to represent "at least" and "at most," the following sentences are written: 

s > and s < 65 

This is an example of a compound inequality. It can be shortened by writing: 

< s < 65 

Example: Graph the solutions to -40 < y < 60. 

Solution: Color in a circle above -40 to represent "less than or equal to." Draw an uncolored circle above 
60. The variable is placed between these two values, so the solutions occur between these two numbers. 

<— I — I 1 1 1 1 • I 1 1 — I 1 1 — I 1 1 — O — I 1 I h- ► 

-100 -90 -80 -70-60-50^0-30 -20 -10 10 20 30 40 50 60 70 80 90 100 

www.ckl2.org 232 



Inequalities Involving "Or" 

A restaurant offers discounts to children 3 years or younger or to adults over 65. Graph the possible ages 
eligible to receive the discount. 

Begin by writing an inequality to represent each piece. "3 years or younger" means you must be born but 
must not have celebrated your fourth birthday. 

< a < 4 

"Adults over 65" implies a > 65. 

The word or between the phrases allows you to graph all the possibilities on one number line. 

Solving "And" Compound Inequalities 

When we solve compound inequalities, we separate the inequalities and solve each of them separately. 
Then, we combine the solutions at the end. 

To solve 3x - 5 < x + 9 < 5x + 13, begin by separating the inequalities. 

3jk - 5 < x + 9 x + 9<5x+13 

2x < 14 and - 4 < 4x 

x < 7 - 1 < i or i > -1 

The answers are x < 7 and x > -1 and can be written as -1 < x < 7. You graph the solutions that satisfy 
both inequalities. 

<— I — I 1 — I I — I — I — I — I » I I — I — I 1 — I — I— O— I — I — !-► 



-10 -9-8-7-6-5-4-3-2-10 1 2 3 4 5 6 7 8 9 10 



Solving "Or" Compound Inequalities 

To solve an "or" compound inequality, separate the individual inequalities. Solve each separately. Then 
combine the solutions to finish the problem. 

To solve 9 - 2x < 3 or 3x + 10 < 6 - x, begin by separating the inequalities. 

9-2x<3 3x+10<6-x 

-2x < -6 or 4x < -4 

x > 3 x < -1 

The answers are x>3orx<-l. 

*— I 1— I \ — I \ 1 1 • I 1 1 1 1 1 1 • I — I 1 !-► 

-5-4-3-2-10 1 2 3 4 5 



Using a Graphing Calculator to Solve Compound Inequalities 

As you have seen in previous lessons, graphing calculators can be used to solve many complex algebraic 
sentences. 

233 www.ckl2.org 



Example: Solve 7x - 2 < lOx + 1 < 9x + 5 using a graphing calculator. 

Solution: This is a compound inequality 7x - 2 < lOx + 1 and lOx + 1 < 9x + 5. 

To enter a compound inequality: 

Press the [Y=] button. 

The inequality symbols are found by pressing [TEST] [2nd] [MATH] 

Enter the inequality as: 



2:* 
3:> 

m 

6:< 



LOGIC 



7i = (7x - 2 < lOx + 1) AND (lOx + 1 < 9x + 5) 



To enter the [AND] symbol, press [TEST]. Choose [LOGIC] on the top row and then select option 1. 



M*ti M*t2 Plot3 

nViB<7X-2<10X+1) 
and (10X+K9X+5 



The resulting graph looks as shown below. 

The solutions are the values of x for which y — 1. 

In this case, -1 < x < 4 . 



www.ckl2.org 



234 



Solve Real- World Compound Inequalities 



m 



""* 



u 



Example: The speed of a golf ball in the air is given by the formula v = -32/ + 80 ; where t is the time 
since the ball was hit. When is the ball traveling between 20 ft/ sec and 30 ft/ sec inclusive'? 

Solution: We want to find the times when the ball is traveling between 20 ft/sec and 30 ft/sec inclusive. 
Begin by writing the inequality to represent the unknown values, 20 < v < 30. 

Replace the velocity formula v = -32/ + 80, with the minimum and maximum values. 

20 < -32/ + 80 < 30 

Separate the compound inequality and solve each separate inequality. 



20 < -32/ + 80 
32/ < 60 

/ < 1.875 



and 



- 32/ + 80 < 30 
50 < 32/ 
1.56 < / 



1.56 < t < 1.875. Between 1.56 and 1.875 seconds, the ball is traveling between 20 ft/sec and 30 ft/sec. 

Inequalities can also be combined with dimensional analysis. 

Example: William's pick-up truck gets between 18 and 22 miles per gallon of gasoline. His gas tank can 
hold 15 gallons of gasoline. If he drives at an average speed of 40 miles per hour, how much driving time 
does he get on a full tank of gas? 




Solution: Use dimensional analysis to get from time per tank to miles per gallon. 



/ k&a? 1 Xetrxfc 40 miles 40/ miles 
x x 



1 temfc 15 gallons 1 h&af 45 gallon 



Since the truck gets between 18 to 22 miles/gallon, you can write a compound inequality. 

40/ 

18 < — < 22 

15 



235 



www.ckl2.org 



Separate the compound inequality and solve each inequality separately. 

40? 



18 < 

15 

270 < 40? 
6.75 < ? 



and 



40? 



<22 



15 

40? < 330 

? < 8.25 



William can drive between 6.75 and 8.25 hours on a full tank of gas. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Compound Inequalities (11:45) 




Figure 6.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/769 



1. Describe the solution set to a compound inequality joined by the word "and." 

2. How would your answer to question #1 change if the joining word was "or." 

3. Write the process used to solve a compound inequality. 

Write the compound inequalities represented by the following graphs. 



4 - <4— I — I — I — I — I — I • I — I — \- 



H — I 1 — I — O — I — I — h 



-100 -90 -80-70 -60 -50 ^10 -30 -20 -10 10 20 30 40 50 60 70 80 90 100 
5 <4— I — I — I — I — I — I — I — I— O—l — I — I — I — I — I » I — I — I — I — \ 



-10 -9-8-7-6-5-4-3-2-1 1 2 3 4 5 6 7 8 9 10 
6 ««— I — I— O—l — I — I — I — I— I — I— O—l — I — I — I — I — I — I — I — I — h- 



-10 -9-8-7-6-5-4-3-2-10 1 2 3 4 5 6 7 8 9 10 
7 - <4—\ — I — I — I — I — I • I — I — I — I — I — I— O—l — I — I — I — I — I — I- 



-5-4-3-2-1012345 
<— I 1 1 1 1— O—l — I 1 — I — I 1 1 1 — I— O—l 1 1 1 h 



-50^5^10-35-30-25-20-15-10-5 5 10 15 20 25 30 35 40 45 50 



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236 



9 <4— I — I — I — I — I — I — I — I— I — •— I — I — I — I • I — I — I — I — I — !-► 
-10 -9-8-7-6-5-4-3-2-1 1 2 3 4 5 6 7 8 9 10 

10 - <4— I — I — I — I — I — I — — I — I — I — I — \—0—\ 1 — I — I — I — I — I — !-► 

-5-4-3-2-1012345 

Graph each compound inequality on a number line. 

11. -4<x<6 

12. i<0ori>2 

13. x > -8 or x < -20 

14. -15<x<85 

In 15 - 30, solve the following compound inequalities and graph the solution on a number line. 

15. -5<x-4< 13 

16. -2<4x-5< 11 

17. *z2 < 2x - 4 or *z2 > x + 5 

18. 1 <3jc + 4<4 

19. -12<2-5x<7 

20. | < 2x + 9 < § 

21. -2^- < -1 

22. 5jc + 2(x-3) >2 

23. 3x + 2 < 10 or 3x + 2 > 15 

24. 4x - 1 > 7 or ^ < 3 

25. 3-x< -4 or 3-x> 10 

26. ^ <2or-f + 3§ 

27. 2x-7< -3 or 2jc-3> 11 

28. -6d>48 or 10 + d > 11 

29. 6 + &<8orZ? + 6>6 

30. 4x + 3 < 9 or -5x + 4 < -12 

31. Using the golf ball example, find the times in which the velocity of the ball is between 50 ft/ sec and 
60 ft/sec. 

32. Using the pick-up truck example, suppose William's truck has a dirty air filter, causing the fuel 
economy to be between 16 and 18 miles per gallon. How many hours can William drive on a full 
tank of gas using this information? 

33. To get a grade of B in her Algebra class, Stacey must have an average grade greater than or equal 
to 80 and less than 90. She received the grades of 92, 78, and 85 on her first three tests. Between 
which scores must her grade fall on her last test if she is to receive a grade of B for the class? 

Mixed Review 

34. Solve the inequality and write its solution in interval notation: ^^ < -4. 

35. Graph 2x - 2y = 6 using its intercepts. 

36. Identify the slope and y-intercept of y + 1 = |(jc - 5). 

37. A yardstick casts a one-foot shadow. What is the length of the shadow of a 16-foot tree? 

38. George rents videos through a mail-order company. He can get 16 movies each month for $16.99. 
Sheri rents videos through instant watch. She pays $1.99 per movie. When will George pay less than 
Sheri? 

237 www.ckl2.org 



39. Evaluate: -l\ + if. 

40. Find a line parallel to y — 5x - 2 containing (1, 1). 

6.5 Absolute Value Equations 

In Chapter 2, this textbook introduced the operation absolute value. The absolute value of a number is 
the distance from zero on a number line. The numbers 4 and -4 are each four units away from zero on a 
number line. So, |4| = 4 and | - 4| = 4. 

Below is a more formal definition of absolute value. 

For any real number jc, 

\x\ = x for all x > 

\x\ = -x(read the opposite of jc) for all x < 

The second part of this definition states that the absolute value of a negative number is its opposite (a 
positive number). 

Example 1: Evaluate \ - 120|. 

Solution: The absolute value of a negative number is its inverse, or opposite. Therefore, | - 120| = 
-(-120) = 120. 

Because the absolute value is always positive, it can be used to find the distance between two values on a 
number line. 

The distance between two values x and y on a number line is found by: 

distance = \x — y\ or \y - x\ 

Example 2: Find the distance between -5 and 8. 

Solution: Use the definition of distance. Let x — -5 and y — 8. 

distance = | - 5 - 8| = | - 13| 
The absolute value of -13 is 13, so -5 and 8 are 13 units apart. 

Solving an Absolute Value Equation 

Absolute value situations can also involve unknown variables. For example, suppose the distance from zero 
is 16. What two points can this represent? 

Begin by writing an absolute value sentence to represent this situation. 

16 = \n\, where n = the missing value 

Which two numbers are 16 units from zero? 

n = 16 or n = -16 

Absolute value situations can also involve distance from points other than zero. We treat such cases as 
compound inequalities, separating the two independent equations and solving separately. 

www.ckl2.org 238 



Example 3: Solve for x : \x - 4| = 5. 

Solution: This equation looks like the distance definition 

distance = \x - y\ or \y - x\ 

The distance is 5, and the value of y is 4. We are looking for two values that are five units away from four 
on a number line. 

Visually, we can see the answers are -1 and 9. 

Algebraically, we separate the two absolute value equations and solve. 

x - 4 = 5 and x - 4 = -(5) 

By solving each, the solutions become: 

x = 9 and x = -1 

Solve |2x-7| = -6. 

Begin by separating this into its separate equations. 

2x - 7 = -6 and 2x - 7 = -(-6) = 6 

Solve each equation independently. 

2x - 7 = 6 2x - 7 = -6 

2x -7 + 7 = 6 + 7 2jc-7 + 7 = -6 + 7 

2x = 13 2x = 1 

13 1 

x = ~ir x = :t 

2 2 

Example: ^4 company packs coffee beans in airtight bags. Each bag should weigh 16 ounces but it is hard to 
fill each bag to the exact weight. After being filled, each bag is weighed and if it is more than 0.25 ounces 
overweight or underweight, it is emptied and repacked. What are the lightest and heaviest acceptable bags? 




Figure 6.5 

Solution: The varying quantity is the weight of the bag of coffee beans. Choosing a letter to represent this 
quantity and writing an absolute value equation yields: 

239 www.ckl2.org 



[w — 16| = 0.25 

Separate and solve. 

w- 16 = 0.25 w-16 = -0.25 

w = 16.25 w = 15.75 

The lightest bag acceptable is 15.75 ounces and the heaviest bag accepted is 16.25 ounces. 

Graphing an Absolute Value Equation 

Absolute value equations can be graphed in a way that is similar to graphing linear equations. By making 
a table of values, you can get a clear picture of what an absolute value equation will look like. 

Example: Graph the solutions to y = \x - 1|. 

Solution: Make a table of values and plot the ordered pairs. 

Table 6.1: 

x y — \x-l\ 

-2 |-2-l| = 3 

-1 | - 1 - 1| = 2 

|0-1| = 1 

1 H -H=o 

2 |2-1| = 1 

3 |3-1| = 2 

Every absolute value graph will make a "V"-shaped figure. It consists of two pieces: one with a negative 
slope and one with a positive slope. The point of their intersection is called the vertex. An absolute value 
graph is symmetrical, meaning it can be folded in half on its line of symmetry. 

Absolute value equations can always be graphed by making a table of values. However, you can use the 
vertex and symmetry to help shorten the graphing process. 

Step 1: Find the vertex by determining which value of x makes the distance zero. 

Step 2: Using this value as the center of the x- values, choose several values greater than this value and 
several values less than this value. 

Example: Graph y — \x + 5|. 

Solution: Determine which x-value equals a distance of zero. 

= |x + 5| 

x = -5 

Therefore, (-5, 0) is the vertex of the graph and represents the center of the table of values. 
Create the table and plot the ordered pairs. 



www.ckl2.org 240 



Table 6.2: 



y = |x + 5| 



-6 

-5 
-4 
-3 



-7 + 5| = 2 

-6 + 5| = l 

- 5 + 5| = 

-4 + 5| = l 

-3 + 5| = 2 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Absolute Value Equations (10:41) 



Video 



Figure 6.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/770 

Evaluate the absolute value. 

1. |250| 

2. |-12| 

4 - Iral 

Find the distance between the points. 

5. 12 and -11 

6. 5 and 22 

7. -9 and -18 

8. -2 and 3 

9. | and -11 

10. -10.5 and -9.75 

11. 36 and 14 

In 12 - 22, solve the absolute value equations and interpret the results by graphing the solutions on the 
number line. 



241 



www.ckl2.org 



12. |x-5| = 10 

13. |5r - 6| = 9 

14. 1 = I6+54 

15. |8x| = 32 

16. |f| = l 

17. |x + 2| = 6 

18. |5x-2| = 3 

19. 51 = |1-5*| 

20. 8 = 3 + |10y + 5| 

21. |4x-l| = 19 

22. 8|x + 6| = -48 

23. What two features of an absolute value graph help determine the appropriate x- values to use for a 
table? 

24. The vertex of an absolute value equation is (0.5, 0). Give several x- values that would be appropriate 
for a table. 

In 25-35, graph the function. 

25. v = |x + 3| 

26. y = \x-6\ 

27. y = \4x + 2| 

28. y = |f -4| 

29. |x-4|=y 

30. -|x-2| = v 

31. y = |x| - 2 

32. y = \x\ + 3 

33. y = \\x\ 

34. y = 4|x| - 2 

35. y = \hx\ + 6 

36. A company manufactures rulers. Their 12-inch rulers pass quality control if they within ^ inches of 
the ideal length. What is the longest and shortest ruler that can leave the factory? 

Mixed Review 

37. Solve: 6/ - 14 < 2t + 7. 

38. The speed limit of a semi-truck on the highway is between 45 mph and 65 mph. 

(a) Write this situation as a compound inequality 

(b) Graph the solutions on a number line. 

39. Lloyd can only afford transportation costs of less than $276 per month. His monthly car payment is 
$181 and he sets aside $25 per month for oil changes and other maintenance costs. How much can 
he afford for gas? 

40. Simplify Vl2x V3. 

41. A hush puppy recipe calls for 3.4 ounces of flour for one batch of 8 hush puppies. You need to make 
56 hush puppies. How much flour do you need? 

42. What is the additive inverse of 124? 

43. What is the multiplicative inverse of 14? 

44. Define the Addition Property of Equality. 

www.ckl2.org 242 



6.6 Absolute Value Inequalities 

An absolute value inequality is a combination of two concepts: absolute values and linear inequalities. 
Therefore, to solve an absolute value inequality, you must use the problem-solving methods of each concept. 

• To solve an absolute value equation, use the definition. 

— If d = \x - a\, then x - a = d OR x - a = -d. 

• To solve a linear inequality, use the concepts learned in Lessons 2 and 3 of this chapter. 

— Remember, when dividing by a negative, the inequality symbol must be reversed! 

Let's begin by looking at an example. 

|x|<3 

Since \x\ represents the distance from zero, the solutions to this inequality are those numbers whose distance 
from zero is less than or equal to 3. The following graph shows this solution: 

^— I 1 1 1 • I 1 — I 1 1 1 1 1 — I 1 1 • I — I 1 !-► 

-5-4-3-2-1012345 

Notice that this is also the graph for the compound inequality -3 < x < 3. 
Below is a second example. 

|x|>2 

Since the absolute value of x represents the distance from zero, the solutions to this inequality are those 
numbers whose distance from zero are more than 2. The following graph shows this solution. 

+— I 1 — I 1 1 — I— O— I 1 1 1 1 1 — I— O^H 1 1 — I 1 !-► 

-5-4-3-2-1 1 2 3 4 5 

In general, the solutions to absolute value inequalities take two forms: 

1. If |jc| < a, then x < a or x > -a. 

2. If \x\ > a, then x > a or x < -a. 

Example 1: Solve \x + 5| > 7. 

Solution: This equation fits situation 2. Therefore, x + 5 > 7 OR x + 5 < -7 

Solve each inequality separately. 

x + 5>7 x + 5<-7 

x> 2 x<-12 

The solutions are all values greater than two or less than -12. 

Example: The velocity of an object is given by the formula v = 25t - 80 ; where the time is expressed in 
seconds and the velocity is expressed in feet per second. Find the times when the velocity is greater than or 
equal to 60 feet per second. 

243 www.ckl2.org 



Solution: We want to find the times when the velocity is greater than or equal to 60 feet per second. Using 
the formula for velocity v = 25t- 80 and substituting the appropriate values, we obtain the absolute value 
inequality \25t - 80| > 60 

This is an example like case 2. Separate and solve. 

25/ - 80 > 60 or 25/ - 80 < -60 

25/ > 140 or 25/ < 20 

/ > 5.6 or / < 0.8 

Multimedia Links: For more assistance with graphing absolute value inequalities, visit this YouTube 
video: 

Algebra - Inequalities with Absolute Value 




Figure 6.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/771 

Or you can also visit this link on TheMathPage: http://www.themathpage.com/alg/absolute-value. 
htm. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Absolute Value Inequalities (3:26) 




Figure 6.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/772 



1. You are asked to solve \a + 1| < 4. What two inequalities does this separate into? 



In 2 - 21, solve the inequality and show the solution graph. 
www.ckl2.org 244 



2. 


x|<6 


3. 


4 < |a + 4| 


4. 


x| > 3.5 


5. 


6 > |10fc + 6| 


6. 


x\< 12 


7. 
8. 


isl< 2 


9. 


7x| > 21 


10. 


6c + 5| < 47 


11. 


x-5|>8 


12. 


x + 7| < 3 


13. 

14. 


2x-5|> 13 


15. 


5x + 3|<7 


16. 


f-4|<2 


17. 


2* i ql > 5 

7 ^ v \ * 7 


18. 


-6/ + 3| + 9> 18 


19. 


9p + 5| > 23 


20. 
21. 


-2s-4|<6 

H0m-5| ^ k 
8 > D 


22. 


A three-month-olc 



A three-month-old baby boy weighs an average of 13 pounds. He is considered healthy if he is 2.5 
pounds more or less than the average weight. Find the weight range that is considered healthy for 
three-month-old boys. 



Mixed Review 



23. Solve |7i*| = 77. 

24. A map has a scale of 2 inch = 125 miles. How far apart would two cities be on the map if the actual 
distance is 945 miles? 

25. Determine the domain and range: {(-9, 0), (-6, 0), (-4, 0), (0, 0), (3, 0), (5, 0)}. 

26. Is the relation in question #25 a function? Explain your reasoning. 

27. Consider the problem 3(2x - 7) = 100. Lei says the first step to solving this equation is to use the 
Distributive Property to cancel the parentheses. Hough says the first step to solving this equation is 
to divide by 3. Who is right? Explain your answer. 

28. Graph 4x + y = 6 using its intercepts. 

29. Write ^ as a percent. Round to the nearest hundredth. 

30. Simplify -5| -f ^. 



6.7 Linear Inequalities in Two Variables 

When a linear equation is graphed in a coordinate plane, the line splits the plane into two pieces. Each 
piece is called a half plane. The diagram below shows how the half planes are formed when graphing a 
linear equation. 

245 www.ckl2.org 




A linear inequality in two variables can also be graphed. Instead of graphing only the boundary line 
(y = mx + ft), you must also include all the other ordered pairs that could be solutions to the inequality. 
This is called the solution set and is shown by shading, or coloring, the half plane that includes the 
appropriate solutions. 

When graphing inequalities in two variables, you must remember when the value is included (< or >) or 
not included (< or >). To represent these inequalities on a coordinate plane, instead of shaded or unshaded 
circles, we use solid and dashed lines. We can tell which half of the plane the solution is by looking at the 
inequality sign. 

• > The solution is the half plane above the line. 

• > The solution is the half plane above the line and also all the points on the line. 

• < The solution is the half plane below the line. 

• < The solution is the half plane below the line and also all the points on the line. 

The solution of y > mx + b is the half plane above the line. The dashed line shows that the points on the 
line are not part of the solution. 











v a 


k 


















5 

A - 








/ 












4 








/ 
/ 












3 
1 _ 






/ 

i 














i _ 






t 
> 














1 




i 
1 









< r 



T^-l 1 1 1 V 

L 2 ? 4 f i x 



■5 -4 -3 -2 -1 



y>mx + 



www.ckl2.org 



246 



The solution of y > mx + b is the half plane above the line and all the points on the line. 




The solution of y < mx + b is the half plane below the line. 

y. 

5 
4 
3 

2 
1 



5 -4 -3 -2 -1 



3t| 

y < mx + b ' 



LA 



-4 



/, 



-H 1 1 1 ► 

1/234 5 x 



The solution of y < mx + b is the half plane below the line and all the points on the line. 



247 



www.ckl2.org 




Example 1: Graph the inequality y > 2x - 3. 

Solution: This inequality is in a slope-intercept form. Begin by graphing the line. Then determine the 
half plane to color. 

• The inequality is >, so the line is solid. 

• The inequality states to shade the half plane above the boundary line. 




In general, the process used to graph a linear inequality in two variables is: 
Step 1: Graph the equation using the most appropriate method. 

• Slope-intercept form uses the y-intercept and slope to find the line. 

• Standard form uses the intercepts to graph the line. 

• Point-slope uses a point and the slope to graph the line. 

Step 2: If the equal sign is not included, draw a dashed line. Draw a solid line if the equal sign is included. 
www.ckl2.org 248 



Step 3: Shade the half plane above the line if the inequality is "greater than." Shade the half plane under 
the line if the inequality is "less than." 

Example: A pound of coffee blend is made by mixing two types of coffee beans. One type costs $9.00 per 
pound and another type costs $7.00 per pound. Find all the possible mixtures of weights of the two different 
coffee beans for which the blend costs $8.50 per pound or less. 

Solution: Begin by determining the appropriate letters to represent the varying quantities. 

Let x = weight of $9.00 per pound coffee beans in pounds and let y = weight of $7.00 per pound coffee 
beans in pounds. 

Translate the information into an inequality. 9x + 7y < 8.50. 

Because the inequality is in standard form, it will be easier to graph using its intercepts. 



JQ 

£ 

O 



1 





y a 


i 
















































1 


£o - 
























1 


.O 

A 
























.2 - 
























1 


s 






















).8- 




\ 




















I 




S 


\ 


















c 


).6 " 

)A 

\ i - 






\ 


\ 
















c 

f 








\ 
















I 


l.Z ~ 










\ 
















r 


■ III' 

0.2 0.4 0.6 0.8 ' 




1. 


2 1 


.4 1 


.6 




— ► 

X 



















weight of $9 coffee beans 

When x = 0,v = 1.21. When y = 0,x = 0.944. 

Graph the inequality. The line will be solid. We shade below the line. 

We graphed only the first quadrant of the coordinate plane because neither bag should have a negative 
weight. 

The blue-shaded region tells you all the possibilities of the two bean mixtures that will give a total less 
than or equal to $8.50. 

Example 2: Julian has a job as an appliance salesman. He earns a commission of $60 for each washing 
machine he sells and $130 for each refrigerator he sells. How many washing machines and refrigerators 
must Julian sell to make $1,000 or more in commission? 

Solution: Determine the appropriate variables for the unknown quantities. Let x = number of washing 
machines Julian sells and let y = number of refrigerators Julian sells. 

Now translate the situation into an inequality. 60x + 130y > 1,000. 

Graph the standard form inequality using its intercepts. When x = 0,y = 7.692. When y = 0, x = 16.667. 
The line will be solid. 

We want the ordered pairs that are solutions to Julian making more than $1,000, so we shade the half 
plane above the boundary line. 



249 



www.ckl2.org 



cu 
en 



QJ 



£ 



y * 


L 






















20 " 
























18 " 
16 - 

14 - 
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1 z 

10 - 
8 - 
6 - 


























































































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2 - 












































► 



2 4 6 8 10 12 14 16 18 20 

I I I I I I I I I I I 



number of washing machines 



Graphing Horizontal and Vertical Linear Inequalities 



Linear inequalities in one variable can also be graphed in the coordinate plane. They take the form of 
horizontal and vertical lines, however the process is identical to graphing oblique, or slanted, lines. 

Example: Graph the inequality x > 4 on: 1) a number line and 2) the coordinate plane. 

Solution: Remember what the solution to x > 4 looks like on a number line. 

<— I — I 1 — I 1 1 — I — I — I — I — I 1 — I — I — — I — I — I 1 — I — !-► 

-10 -9-8-7-6-5-4-3-2-10 1 2 3 4 5 6 7 8 9 10 

The solution to this inequality is the set of all real numbers x that are bigger than four but not including 
four. 

On a coordinate plane, the line x = 4 is a vertical line four units to the right of the origin. The inequality 
does not equal four, so the vertical line is dashed. This shows the reader that the ordered pairs on the 
vertical line x = 4 are not solutions to the inequality. 

The inequality is looking for all x-coordinates larger than four. We then color the half plane to the right, 
symbolizing x > 4. 



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250 



10 
8 
6 
4 
2 



— i 1— 

-10 -8 -6 -4 -2 



10 



—I 1 1 1— 

2 4 6 8 10 



Graphing absolute value inequalities can also be done in the coordinate plane. To graph the inequality 
|jc| > 2, we remember Lesson 6.6 and rewrite the absolute value inequality. 

x < -2 or x > 2 

Then graph each inequality on a coordinate plane. 

In other words, the solution is all the coordinate points for which the value of x is smaller than or equal to 
-2 and greater than or equal to 2. The solution is represented by the plane to the left of the vertical line 
x = -2 and the plane to the right of line x = 2. 

Both vertical lines are solid because points on the line are included in the solution. 



n 1 i r 

10 -8 -6 -4 



10 
8H 

6 
4 
2 



n 1 r~ 

6 8 10 




-2- 

-4- 

-6- 

-8- 

10- 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 



251 



www.ckl2.org 



same in both. 

CK-12 Basic Algebra: Graphing Inequalities (8:03) 




Figure 6.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/773 



1. Define half plane. 

2. In which cases would the boundary line be represented by a dashed line? 

3. In which cases would the boundary line be represented by a solid line? 

4. What is a method to help you determine which half plane to color? 

In 5 - 26, graph each inequality in a coordinate plane. 



5. x<20 

6. y >-5 

7. y <6 

8. |jc| > 10 

9. \y\ < 7 

10. y <4x + 3 

11. y>-§ -6 

12. y < -|x+5 

13. 3x-4y> 12 

14. x + 7y < 5 

15. y < -4x + 4 

16. y > lx + 3 

17. 6x + 5y > 1 

18. 6x-5y< 15 

19. 2x-y <5 

20. y + 5<-4x+10 

21. x- \y > 5 

22. y + 4<-f + 5 

23. 5x-2y>4 

24. 30x + 5y < 100 

25. v > -x 

26. 6x-y <4 

27. Lili can make yarn ankle bracelets and wrist bracelets. She has 600 yards of yarn available. It takes 
6 yards to make one wrist bracelet and 8 yards to make one ankle bracelet. Find all the possible 
combinations of ankle bracelets and wrist bracelets she can make without going over her available 
yarn. 

28. An ounce of gold costs $670 and an ounce of silver costs $13. Find all possible weights of silver and 
gold that makes an alloy (combination of metals) that costs less than $600 per ounce. 



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252 



29. A phone company charges 50 cents per minute during the daytime and 10 cents per minute at night. 
How many daytime minutes and nighttime minutes would you have to use to pay more than $20.00 
over a 24-hour period? 

30. Jesu has $30 to spend on food for a class barbeque. Hot dogs cost $0.75 each (including the bun) 
and burgers cost $1.25 (including bun and salad). Plot a graph that shows all the combinations of 
hot dogs and burgers he could buy for the barbecue, spending less than $30.00. 

31. At the local grocery store, strawberries cost $3.00 per pound and bananas cost $1.00 per pound. If 
I have $10 to spend between strawberries and bananas, draw a graph to show what combinations of 
each I can buy and spend at most $10. 

Mixed Review 

33. Graph y = 3\x - 3|. 

34. Graph y= fx-2. 

35. What is 14.75% of 29? 

36. A shirt was sold for $31.99 after a 15% markup. What was the original price? 

37. Using the formula to convert Celsius to Fahrenheit found in Lesson 4.7, determine the Fahrenheit 
equivalent to 16°C. 

38. Charlene has 18 more apples than Raul. Raul has 36 apples. Write an equation to represent this 
situation and determine how many apples Charlene has. 

39. Suppose you flip a coin. What are its possible outcomes? 

40. How many degrees are in a circle? 

6.8 Theoretical and Experimental Probability 

So far in this text, you have solved problems dealing with definite situations. In the next several chapters, 
we will begin to look at a branch of mathematics that deals with possible situations. The study of 
probability involves applying formulas to determine the likelihood of an event occurring. 

Almost all companies use some form of probability. Automotive companies want to determine the likelihood 
of their new vehicle being a big seller. Cereal manufacturers want to know the probability that their cereal 
will sell more than the competition. Pharmaceutical corporations need to know the likelihood of a new 
drug harming those who take it. Even politicians want to know the probability of receiving enough votes 
to win the election. 




Figure 6.10 

Probabilities can start with an experiment. As you learned in a previous chapter, an experiment is a 
controlled study. For example, suppose you want to know if the likelihood, or probability, of getting tails 

253 www.ckl2.org 



when flipping a coin is actually \ . By randomly grabbing a penny and making a tally chart of heads and 
tails, you are performing an experiment. 

The set of all possible outcomes is called the sample space of the experiment. 

The sample space for tossing a coin is {heads, tails}. 

Example 1: List the sample space for rolling a die. 

Solution: A die is a six-sided figure with dots representing the numbers one through six. So the sample 
space is all the possible outcomes (i.e., what numbers could possibly be rolled). 

S ={1,2,3,4,5,6,} 

Once you have determined the number of items in the sample space, you can compute the probability of 
a particular event. 

Any one possible outcome of the experiment is called an event. 

Theoretical probability is a ratio expressing the ways to be successful to the total events in an experi- 
ment. A shorter way to write this is: 

_ number of ways to get success 

Probability [success) = 



total number of possible outcomes 
Probabilities are expressed three ways: 

• As a fraction 

• As a percent 

• As a decimal 

Suppose you wanted to know the probability of landing a head or a tail when flipping a coin. 
There would be two ways to get success and two possible outcomes. 

Pi success) = - = 1 
v ; 2 

This is a very important concept of probability. 

The sum of individual event probabilities has a sum of 100%, or 1. 

Example 2: Determine the theoretical probability of rolling a five on a die. 

Solution: There are six events in the sample space. There is one way to roll a five. 

Ptrolling a 5) = - * 16.67% 
6 

Conducting an Experiment 

Conducting an experiment for probability purposes is also called probability simulation. Suppose you 
wanted to conduct the coin experiment in the lesson opener. By grabbing a random coin, flipping it, and 
recording what lands up is a probability simulation. You can also simulate an experiment using a graphing 
calculator application. 

www.ckl2.org 254 



Performing an Experiment Using the TI-84 Graphing Calculator 

There is an application on the TI calculators called the coin toss. Among others (including the dice roll, 
spinners, and picking random numbers), the coin toss is an excellent application for when you what to find 
the probabilities for a coin tossed more than four times or more than one coin being tossed multiple times. 



Si mulati on 

OfiToss Coins 
Z7Roll Dice 
3. Pick Marbles 
4. Spin Spinner 
5. Draw Cards 
6. Random Numbers 

"OK I lOFTnlhiEDUTlQUIT 



: 



Key Pf ess History Large Screen 



□CJJCZ) 



GD GD (EE) ® 



Let's say you want to see one coin being tossed one time. Here is what the calculator will show and the 
key strokes to get to this toss. 



o 










T H 


ESC 1 +1 1 +10 l+F ■■'} I'ILEhF; 



Key Pr « a History Lar ge Scr «n 



DQ 

[enter] (wJhpcw) 



Let's say you want to see one coin being tossed ten times. Here is what the calculator will show and the 
key strokes to get to this sequence. Try it on your own. 

















T H 


ESC ITQSSISET iDATAlTfiBL 



Key Pre» History Large Screen 



OCDQ 

[ w ] f~^~) [enter] [enter] 
[emter] fwoJTl [ 1 ] [ ] 
[graph] fowpow] 



We can actually see how many heads and tails occurred in the tossing of the 10 coins. If you click on the 
right arrow (>) the frequency label will show you how many of the tosses came up heads. 



FF;EQ:b 



S5H 




iKES- 



T H 
ESC lTDfSlSET IDATAITABL 



Using this information, you can determine the experimental probability of tossing a coin and seeing a 
tail on its landing. 

The experimental probability is the ratio of the proposed outcome to the number of experiment trials. 



255 



www.ckl2.org 



P(success) = 



number of times the event occurred 
total number of trials of experiment 



Example 3: Compare the theoretical probability of flipping a tail to the experimental probability of flipping 
a tail on a coin. 

Solution: There are two events in the sample space. There is one way to flip a tail. 

P(f lipping a tail) = - 

The coin toss simulation the calculator performed stated there were six tails out of ten tosses. 

6 
P(f lipping a tail) = — 

The experimental probability (60%) in this case is greater than the theoretical probability (50%). 



Finding Odds For and Against 

Odds are similar to probability with the exception of the ratio's denominator. 

The odds in favor of an event is the ratio of the number of successful events to the number of non- 
successful events. 



Odds (success) 



number of ways to get success 



number of ways to not get success 
For example, suppose we were interested in the odds of rolling a 5 on a die. 



odds{5) = — 



y 



There is only 1 "5" on the die so there 
is only one way to get success 



There are 5 other possible outcomes 
other than "5": 

"1'\"2V'3", "4", "6" 



What if we were interested in determining the odds against rolling a 5 on a die. There are five outcomes 
other than a "5" and one outcome of a "5." 



Odds against rolling a 5 = - 

Example 4: Find the odds against rolling a number larger than 2 on a standard die. 
www.ckl2.org 256 



Solution: There are four outcomes on a standard die larger than 2 : {3,4,5,6}. 

2 
Odds against rolling > 2 = - 

Notice the "odds against" ratio is the reciprocal of the "odds in favor" ratio. 

Practice Set 

1. Define experimental probability. 

2. How is experimental probability different from theoretical probability? 

3. Complete the table below, converting between probability values. 

Table 6.3: 
Fraction Decimal Percent 



0.015 
j_ 

¥ 

62% 
0.73 



Use the "SPINNER" application in the Probability Simulator for the following questions. Set the spinner 
to five pieces. 

4. What is the sample space? 

5. Find the theoretical probability P(spinng a 4). 

6. Conduct an experiment by spinning the spinner 15 times and recording each number the spinner 
lands on. 

7. What is the experimental probability P(spinng a 4)? 

8. Give an event with a 0% probability. 

In 9 - 18, use a standard 52-card deck to answer the questions. 

9. How many values are in the sample space? What could be an easy way to list all these values? 

10. Determine P(King). 

11. What are the odds against drawing a face card? 

12. What are the odds in favor of drawing a six? 

13. Determine P(Diamond). 

14. Determine P(Nine of Clubs). 

15. Determine P(King or 8 of Hearts). 

16. What are the odds against drawing a spade? 

17. What are the odds against drawing a red card? 

18. Give an event with 100% probability. 

19. Jorge says it has a 60% chance of raining tomorrow. Is this a strong likelihood? Explain your 
reasoning. 



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20. What is the probability there will be a hurricane in your area tomorrow? Why did you choose this 
percentage? 

Consider flipping two coins at the same time. 

21. Write the sample space. 

22. What is the probability of flipping one head and one tail? 

23. What is P(both heads)! 

24. Give an event with 100% probability. 

25. Conduct the experiment 20 times. Find the experimental probability for flipping both heads. Is this 
different from the theoretical probability? 

Mixed Review 

26. Graph the following inequality on a number line -2 < w < 6. 

27. Graph the inequality on a coordinate plane -2 < w < 6. 

28. Solve and graph the solutions using a number line: \n — 3| > 12. 

29. Is n = 4.175 a solution to \n - 3| > 12? 

30. Graph the function g(x) = \x - 8. 

31. Explain the pattern: 24, 19, 14, 9,.... 

32. Simplify (-3) (»*). 

6.9 Chapter 6 Review 

Vocabulary - In 1 - 12, define the term. 

1. Algebraic inequality 

2. Interval notation 

3. Intersection of sets 

4. Union of sets 

5. Absolute value 

6. Compound inequality 

7. Boundary line 

8. Half plane 

9. Solution set 

10. Probability 

11. Theoretical probability 

12. Experimental probability 

13. Find the distance between 16 and 104 on a number line. 

14. Shanna needed less than one dozen eggs to bake a cake. Write this situation as an inequality and 
graph the appropriate solutions on a number line. 

15. Yemi can walk no more than 8 dogs at once. Write this situation as an inequality and graph the 
appropriate solutions on a number line. 

In 16-35, solve each inequality. Graph the solutions on a number line. 

16. y + 7>36 

www.ckl2.org 258 



17. 16* < 1 

18. y - 64 < -64 

19. 5 > | 

20. 0<6-& 
21- -fg<12 

22. 10 > ^ 

23. -14 + m> 7 

24. 4>J+11 

25. f-9<-100 

26. f < -2 

27. 4x > -4 and f < 

28. w-1 <-5or | >-l 

29. | > -2 and -5« > -20 

30. -35 + 3x>5(x-5) 

31. x + 6 - Hjc > -2(3 + 5x) + 12(x + 12) 

32. -64 < 8(6 + 2k) 

33. 0>2(x + 4) 

34. -4(2n - 7) < 37 - 5n 

35. 6£ + 14<-8(-5£-6) 

36. How many solutions does the inequality 6& + 14 < -8(-5fe - 6) have? 

37. How many solutions does the inequality 6x + 11 < 3(2x - 5) have? 

38. Terry wants to rent a car. The company he's chosen charges $25 a day and $0.15 per mile. If he 
rents is for one day, how many miles would he have to drive to pay at least $108? 

39. Quality control can accept a part if it falls within +0.015 cm. The target length of the part is 15 cm. 
What is the range of values quality control can accept? 

40. Strawberries cost $1.67 per pound and blueberries cost $1.89 per pound. Graph the possibilities that 
Shawna can buy with no more than $12.00. 

Solve each absolute value equation. 

41. 24 = |8z| 

42. ||| = -1.5 

43. 1 = |4r - 7| - 2 

44. |-9 + x| = 7 

Graph each inequality or equation. 

45. y = \x\ - 2 

46. y = -|x + 4| 

47. y = |x + l| + l 

48. y > -x + 3 

49. y < -3x + 7 

50. 3x + y<-4 
51.y>=±x + 6 

52. 8x-3y<-12 

53. x < -3 

54. v > -5 

55. -2<x<5 

56. 0<y<3 

259 www.ckl2.org 



57. |*| > 4 

58. |y|<-2 

A spinner is divided into eight equally spaced sections, numbered 1 through 8. Use this information to 
answer the following questions. 

59. Write the sample space for this experiment. 

60. What is the theoretical probability of the spinner landing on 7? 

61. Give the probability that the spinner lands on an even number. 

62. What are the odds for landing on a multiple of 2? 

63. What are the odds against landing on a prime number? 

64. Use the TI Probability Simulator application "Spinner." Create an identical spinner. Perform the 
experiment 15 times. What is the experimental probability of landing on a 3? 

65. What is probability of the spinner landing on a number greater than 5? 

66. Give an event with a 100% probability. 

67. Give an event with a 50% probability. 

6.10 Chapter 6 Test 

1. Consider a standard 52-card deck. Determine: 

(a) P(red4) 

(b) P(purple Ace) 

(c) P(number card) 

2. Solve -7<y + 7< 5 

3. Find the distance between (-1.5 and 9). 

4. Solve 23 = |8 - 7r\ + 3. 

5. Solve | - 7c\ > 49. 

6. Graph x-2y < 10. 

7. Graph y > -|x + 4. 

8. Graph y = -\x - 3|. 

9. A bag contains 2 red socks, 3 blue socks, and 4 black socks. 

(a) If you choose one sock at a time, write the sample space. 

(b) Find P(blue sock). 

(c) Find the odds against drawing a black sock. 

(d) Find the odds for drawing a red sock. 

10. 2(6 + 7r) >-12 + 8r 

11. -56 < 8 + 8(7* + 6) 



Image Sources 



(1) http : //www . publicdomainpictures . net /view- image . php?image=36&#38 ; picture= 
cereals-with-grids&#38 ; large=l. 

(2) http: //www. public- domain- image. com/studio/slides/roasted-cof fee-beans .html. 
www.ckl2.org 260 



Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/ 'flexr/ 'chapter /9616. 



261 www.ckl2.org 



Chapter 7 

Systems of Equations and 
Inequalities; Counting Methods 



James is trying to expand his pastry business to include cupcakes and personal cakes. He has a limited 
amount of manpower to decorate the new items and a limited amount of material to make the new cakes. 
In this chapter, you will learn how to solve this type of situation. 




Every equation and inequality you have studied thus far is an example of a system. A system is a set 
of equations or inequalities with the same variables. This chapter focuses on the methods used to solve 
a system such as graphing, substitution and elimination. You will combine your knowledge of graphing 
inequalities to solve a system of inequalities. 

7.1 Linear Systems by Graphing 

In a previous chapter, you learned that the intersection of two sets is joined by the word "and." This word 
also joins two or more equations or inequalities. A set of algebraic sentences joined by the word "and" is 
called a system. 

The solution (s) to a system is the set of ordered pairs that is in common to each algebraic sentence. 

Example 1: Determine which of the points (1, 3), (0, 2), or (2, 7) is a solution to the following system of 



www.ckl2.org 262 



\y = 4x-l 
equations. < 

\y = 2x + 3 

Solution: A solution to a system is an ordered pair that is in common to all the algebraic sentences. To 
determine if a particular ordered pair is a solution, substitute the coordinates for the variables x and y in 
each sentence and check. 



Check (1, 3) 
Check (0, 2) 
Check (2, 7) 



[ 3 = 4(1) - 1; 3 = 3. Yes, this ordered pairs checks. 

I 3 = 2(1) + 3; 3 = 5. No, this ordered pair does not check. 



1 2 = 4(0) - 1; 2 = -1. No, this ordered pair does not check. 
I 2 = 2(0) + 3; 2 = 3. No, this ordered pair does not check. 

( 7 = 4(2) - 1; 7 = 7. Yes, this ordered pairs checks. 
I 7 = 2(2) + 3; 7 = 7. Yes, this ordered pairs checks. 

Because the coordinate (2, 7) works in both equations simultaneously, it is a solution to the system. 

To determine the coordinate that is in common to each sentence in the system, each equation can be 
graphed. The point at which the lines intersect represents the solution to the system. The solution can 
be written two ways: 

• As an ordered pair, such as (2, 7) 

• By writing the value of each variable, such as x = 2, y = 7 

{y = 3x - 5 
y = -2x + 5 

Solution: By graphing each equation and finding the point of intersection, you find the solution to the 
system. 

Each equation is written in slope-intercept form and can be graphed using the methods learned in Chapter 
4. 

The lines appear to intersect at the ordered pair (2, 1). Is this the solution to the system? 




(1 = 3(2) -5; 1 = 1 

\l = -2(2) + 5; 1 = 1 

(y — 3^ _ g 
y = -2x-\- 5 

( x + y = 2 
Example 2: Solve the system < 

{ y = 3 

Solution: The first equation is written in standard form. Using its intercepts will be the easiest way to 
graph this line. 

263 www.ckl2.org 



The second equation is a horizontal line three units up from the origin. 




2\3 4 

The lines appear to intersect at (-1, 3). 




The coordinate is in common to each sentence and is a solution to the system. 

The greatest strength of the graphing method is that it offers a very visual representation of a system of 
equations and its solution. You can see, however, that determining a solution from a graph would require 
very careful graphing of the lines and is really practical only when you are certain that the solution gives 
integer values for x and y. In most cases, this method can offer only approximate solutions to systems of 
equations. For exact solutions, other methods are necessary. 

Solving Systems Using a Graphing Calculator 

A graphing calculator can be used to find or check solutions to a system of equations. To solve a system 
graphically, you must graph the two lines on the same coordinate axes and find the point of intersection. 
You can use a graphing calculator to graph the lines as an alternative to graphing the equations by hand. 

{y = 3x — 5 
, we will use the graphing calculator to find the 
y = -2x +5 

approximate solutions to the system. 
Floti PlotE Plots 

W1H3X-5 
■xVeB"2X+5 

■xVh = 

\V? = 

Begin by entering the equations into the Y = menu of the calculator. 

You already know the solution to the system is (2, 1). The window needs to be adjusted so an accurate 
picture is seen. Change your window to the default window. 

WINDOW 
Xnin="10 
Xnax=lQ 
Xscl=l 
Vnin=-1@ 
Vnax=10 
Vscl=l 
Xres=i 

See the graphs by pressing the GRAPH button. 
www.ckl2.org 264 




The solution to a system is the intersection of the equations. To find the intersection using a graphing 
calculator, locate the Calculate menu by pressing 2 nd and TRACE. Choose option #5 - INTERSEC- 
TION. 

2=zero 

3:nininun 

4=naxiMun 

5= intersect 

6:dy^dx 

7:Xf<x)dx 

The calculator will ask you "First Curve?" Hit ENTER. The calculator will automatically jump to 
the other curve and ask you "Second Curve?" Hit ENTER. The calculator will ask, "Guess?" Hit 
ENTER. The intersection will appear at the bottom of the screen. 




Intersection 



Example: Peter and Nadia like to race each other. Peter can run at a speed of 5 feet per second and Nadia 
can run at a speed of 6 feet per second. To be a good sport, Nadia likes to give Peter a head start of 20 
feet. How long does Nadia take to catch up with Peter? At what distance from the start does Nadia catch 
up with Peter? 



Sftlsec 




5ftfsec 




20ft 



ratextime. 



Solution: Begin by translating each runner's situation into an algebraic sentence using distance 

Peter: d = 5t + 20 

Nadia: d = 6t 

The question asks when Nadia catches Peter. The solution is the point of intersection of the two lines. 
Graph each equation and find the intersection. 

WINDOW 
Xnin=0 
Xnax=25 
Xscl=5 
Vnin=0 
Vnax=20@ 
Vscl=50 
Xres=l 



265 



www.ckl2.org 




The two lines cross at the coordinate t = 20, d = 120. This means after 20 seconds Nadia will catch Peter. 
At this time, they will be at a distance of 120 feet. Any time after 20 seconds Nadia will be farther from 
the starting line than Peter. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Linear Systems by Graphing (8:30) 




Figure 7.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/774 



1. Define a system. 

2. What is the solution to a system? 

3. Explain the process of solving a system by graphing. 

4. What is one problem with using a graph to solve a system? 

5. What are the two main ways to write the solution to a system of equations? 

6. Suppose Horatio says the solution to a system is (4, -6). What does this mean visually? 

7. Where is the "Intersection" command located in your graphing calculator? What does it do? 

8. In the race example, who is farther from the starting line at 19.99 seconds? At 20.002 seconds? 

Determine which ordered pair satisfies the system of linear equations. 




[5x + 2y = 10 
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;(1,4), (2,9), (i, -\) 
;(8,13), (-7,6), (0,4) 
;(-9,l), (-6,20), (14,2) 



266 



12 £+* = • ; (3, -I), (-4,3), (1,4) 

In 13 - 22, solve the following systems by graphing. 

13. y = x + 3 
y = -x + 3 

14. y = 3x - 6 
y = -x + 6 

15. 2x = 4 
y = -3 

16. y = -x -\- 5 
-x + y = 1 

17. x + 2y = 8 
5jc + 2y = 

18. 3x + 2y= 12 
4jc - y = 5 

19. 5x + 2y = -4 
x-y = 2 

20. 2;t + 4 = 3y 

x - 2y + 4 = 

21. y = f-3 
2jc - 5y = 5 

22. y = 4 

x = 8 - 3y 

23. Mary's car is 10 years old and has a problem. The repair man indicates that it will cost her $1200.00 
to repair her car. She can purchase a different, more efficient car for $4,500.00. Her present car 
averages about $2,000.00 per year for gas while the new car would average about $1,500.00 per year. 
Find the number of years for when the total cost of repair would equal the total cost of replacement. 

24. Juan is considering two cell phone plans. The first company charges $120.00 for the phone and $30 
per month for the calling plan that Juan wants. The second company charges $40.00 for the same 
phone, but charges $45 per month for the calling plan that Juan wants. After how many months 
would the total cost of the two plans be the same? 

25. A tortoise and hare decide to race 30 feet. The hare, being much faster, decided to give the tortoise 
a head start of 20 feet. The tortoise runs at 0.5 feet/sec and the hare runs at 5.5 feet per second. 
How long will it be until the hare catches the tortoise? 

Mixed Review 

26. Solve for h: 25 >\2h + 5\. 

27. Subtract § - \. 

28. You write the letters to ILLINOIS on separate pieces of paper and place them into a hat. 

(a) Find P(drawing an I). 

(b) Find the odds for drawing an L. 

29. Graph x < 2 on a number line and on a Cartesian plane. 

30. Give an example of an ordered pair in quadrant II. 

31. The data below show the average life expectancy in the United States for various years. 

(a) Use the method of interpolation to find the average life expectancy in 1943. 

267 www.ckl2.org 



(b) Use the method of extrapolation to find the average life expectancy in 2000. 

(c) Find an equation for the line of best fit. How do the predictions of this model compare to your 
answers in questions a) and b)? 

Table 7.1: U. S. Life Expectancy at Birth 



Birth Year 


Ferr 


1940 


65.2 


1950 


71.1 


1960 


73.1 


1970 


74.7 


1975 


76.6 


1980 


77.5 


1985 


78.2 


1990 


78.8 


1995 


78.9 


1998 


79.4 



Male 



Combined 



60.8 
65.6 
66.6 
67.1 
68.6 
70.0 
71.2 
71.8 
72.5 
73.9 



62.9 

68.2 
69.7 
70.8 
72.6 
73.7 
74.7 
75.4 
75.8 
76.7 



7.2 Solving Systems by Substitution 

While the graphical approach to solving systems is helpful, it may not always provide exact answers. There- 
fore, we will learn a second method to solving systems. This method uses the Substitution Property of 
Equality. 

Substitution Property of Equality: If y = an algebraic expression, then the algebraic expression can 
be substituted for any y in an equation or an inequality. 

Consider the racing example from the previous lesson. 

Peter and Nadia like to race each other. Peter can run at a speed of 5 feet per second and Nadia can run 
at a speed of 6 feet per second. To be a good sport, Nadia likes to give Peter a head start of 20 feet. How 
long does Nadia take to catch up with Peter? At what distance from the start does Nadia catch up with 
Peter? 



Sftfsec 




Sfflsec 




The two racers' information was translated into two equations. 

Peter: d = 5t + 20 

Nadia: d = 6t 

We want to know when the two racers will be the same distance from the start. This means we can set 
the two equations equal to each other. 

5^ + 20 = 6; 



Now solve for t. 
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268 



5t - 5t + 20 = 6t - 5t 
20 = It 



After 20 seconds, Nadia will catch Peter. 



Now we need to determine how far from the distance the two runners are. You already know 20 = /, so we 
will substitute to determine the distance. Using either equation, substitute the known value for t and find 
d. 

d = 5(20) + 20^ 120 

When Nadia catches Peter, the runners are 120 feet from the starting line. 

The Substitution Method is useful when one equation of the system is of the form y = algebraic 
expression ori= algebraic expression. 

( x + y = 2 
Example 1: Solve the system < 

{ y = 3 

Solution: The second equation is solved for the variable x. Therefore, we can substitute the value "3" for 
any y in the system. 

x + y = 2 -^ x + 3 = 2 

Now solve the equation for x : 

x+3-3=2-3 

x = -l 

The x-coordinate of the intersection of these two equations is -1. Now we must find the y-coordinate 
using substitution. 

x+y=2^ (-l)+j = 2 

-l + l+y = 2 + l 
y = 3 

As seen in the previous lesson, the solution to the system is (-1, 3). 

(y = 3x - 5 
using substitution. 
y = -2x + 5 

Solution: Each equation is equal to the variable y, therefore the two algebraic expressions must equal each 
other. 

3x - 5 = -2x + 5 
Solve for x. 

3x - 5 + 5 = -2x + 5 + 5 
3x + 2x = -2x + 2x+10 
5x= 10 
x = 2 

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The x-coordinate of the intersection of the two lines is 2. Now you must find the y-coordinate usin^ 
either of the two equations. 

y = -2(2) + 5 = 1 
The solution to the system is x = 2, y = 1 or (2, 1). 



Solving Real- World Systems by Substitution 

Example: Anne is trying to choose between two phone plans. Vendaphone's plan costs $20 per month, with 
calls costing an additional 25 cents per minute. Sellnet's plan charges $40 per month, but calls cost only 
8 cents per minute. Which should she choose? 

Solution: Anne's choice will depend upon how many minutes of calls she expects to use each month. We 
start by writing two equations for the cost in dollars in terms of the minutes used. Since the number of 
minutes is the independent variable, it will be our x. Cost is dependent on minutes. The cost per month 
is the dependent variable and will be assigned y. 



For Vendafone 
For Sellnet 



y = 0.25* + 20 
y = 0.08x + 40 




Minutes used 

By graphing two equations, we can see that at some point the two plans will charge the same amount, 
represented by the intersection of the two lines. Before this point, Sellnet's plan is more expensive. After 
the intersection, Sellnet's plan is cheaper. 

Use substitution to find the point that the two plans are the same. Each algebraic expression is equal to 
y, so they must equal each other. 



0.25.x + 20 = 0.08jc + 40 
0.25jc = 0.08jc + 20 
0.17jc = 20 

x = 117.65 minutes 



Subtract 20 from both sides. 
Subtract 0.08.x from both sides. 
Divide both sides by 0.17. 
Rounded to two decimal places. 



We can now use our sketch, plus this information, to provide an answer. If Anne will use 117 minutes or 
fewer every month, she should choose Vendafone. If she plans on using 118 or more minutes, she should 
choose Sellnet. 



Mixture Problems 



Systems of equations arise in chemistry when mixing chemicals in solutions and can even be seen in things 
like mixing nuts and raisins or examining the change in your pocket! 



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270 



By rearranging one sentence in an equation into y = algebraic expression or x = algebraic expression, you 
can use the Substitution Method to solve the system. 




Image courtesy of Kevin(^ ft ickr.com/creativecommons 

Example: Nadia empties her purse and finds that it contains only nickels and dimes. If she has a total of 
7 coins and they have a combined value of 55 cents, how many of each coin does she have? 

Solution: Begin by choosing appropriate variables for the unknown quantities. Let n = the number of 
nickels and d = the number of dimes. 

There are seven coins in Nadia's purse: n + d = 7. 

The total is 55 cents: 0.05n + Q.lOd = 0.55. 

m [ n +d=7 

The system is: < 

[0.05^ + 0.10^ = 0.55 

We can quickly rearrange the first equation to isolate d, the number of dimes: d = 7 - n. 

Using the Substitution Property, every d can be replaced with the expression 7 - n. 



0.05^ + 0.10(7 -?z) = 0.55 

Now solve for n : 0.05ft + 0.70 - 0.10ft = 0.55 Distributive Property 

-0.05ft + 0.70 = 0.55 Add like terms. 

-0.05ft = -0.15 Subtract 0.70. 

n = 3 Divide by - 0.05. 



Nadia has 3 nickels. There are seven coins in the purse; three are nickels so four must be dimes. 
Check to make sure this combination is 55 cents: 0.05(3) + 0.10(4) = 0.15 + 0.40 = 0.55. 



Chemical Mixtures 

Example: A chemist has two containers, Mixture A and Mixture B. Mixture A has a 60% copper sulfate 
concentration. Mixture B has a 5% copper sulfate concentration. The chemist needs to have a mixture 
equaling 500 mL with a 15% concentration. How much of each mixture does the chemist need? 

271 www.ckl2.org 




F I i ckr. com/creati vcc o mmon s 
Solution: Although not explicitly stated, there are two equations involved in this situation. 

• Begin by stating the variables. Let A = mixture A and 5 = mixture 5. 

• The total mixture needs to have 500 mL of liquid. 

Equation 1 (how much total liquid): A + B = 500. 

• The total amount of copper sulfate needs to be 15% of the total amount of solution (500 mL). 
0.15 • 500 = 75 ounces 

Equation 2 (how much copper sulfate the chemist needs): 0.60A + 0.055 = 75 

U+B = 500 
[0.60A + 0.055 = 75 

By rewriting equation 1, the Substitution Property can be used: A = 500 - B. 
Substitute the expression 500 - B for the variable A in the second equation. 

0.60(500 - B) + 0.055 = 75 

Solve for B. 

300 - 0.605 + 0.055 = 75 Distributive Property 

300 - 0.555 = 75 Add like terms. 

-0.555 = -225 Subtract 300. 
5 « 409 mL 

The chemist needs approximately 409 mL of mixture 5. To find the amount of mixture A, use the first 
equation: A + 409 = 500 

A = 91 mL 

The chemist needs 91 milliliters of mixture A and 409 milliliters of mixture 5 to get a 500 mL solution 
with a 15% copper sulfate concentration. 

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Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Linear Systems by Substitution (9:21) 




Figure 7.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/775 



1. Explain the process of solving a system using the Substitution Property. 

2. Which systems are easier to solve using substitution? 

Solve the following systems. Remember to find the value for both variables! 




273 



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13. x - 3y = 10 
2x + y = 13 



14 



14. Solve the system < f n 



by graphing and substitution. Which method do you prefer? Why? 



15. Of the two non-right angles in a right angled triangle, one measures twice that of the other. What 
are the angles? 




16. The sum of two numbers is 70. They differ by 11. What are the numbers? 

17. A rectangular field is enclosed by a fence on three sides and a wall on the fourth side. The total length 
of the fence is 320 yards. If the field has a total perimeter of 400 yards, what are the dimensions of 
the field? 



wal 



18. A ray cuts a line forming two angles. The difference between the two angles is 18°. What does each 
angle measure? 




19. I have $15.00 and wish to buy five pounds of mixed nuts for a party. Peanuts cost $2.20 per pound. 
Cashews cost $4.70 per pound. How many pounds of each should I buy? 

20. A chemistry experiment calls for one liter of sulfuric acid at a 15% concentration, but the supply 
room only stocks sulfuric acid in concentrations of 10% and in 35%. How many liters of each should 
be mixed to give the acid needed for the experiment? 

21. Bachelle wants to know the density of her bracelet, which is a mix of gold and silver. Density is total 
mass divided by total volume. The density of gold is 19.3 g/cc and the density of silver is 10.5 g/cc. 
The jeweler told her that the volume of silver used was 10 cc and the volume of gold used was 20 cc. 
Find the combined density of her bracelet. 

22. Jeffrey wants to make jam. He needs a combination of raspberries and blackberries totaling six 
pounds. He can afford $11.60. How many pounds of each berry should he buy? 

Mixed Review 

23. The area of a square is 96 inches 2 . Find the length of a square exactly. 

24. The volume of a sphere is V = §tzt 3 , where r = radius. Find the volume of a sphere with a diameter 
of 11 centimeters. 

25. Find: 

(a) the additive inverse and 

(b) the multiplicative inverse of 7.6. 



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274 



26. Solve for x : ^f = 6. 

27. The temperature in Fahrenheit can be approximated by crickets using the rule "Count the number 
of cricket chirps in 15 seconds and add 40." 

(a) What is the domain of this function? 

(b) What is the range? 

(c) Would you expect to hear any crickets at 32°F? Explain your answer. 

(d) How many chirps would you hear if the temperature were 57°C? 

28. Is 4.5 a solution to 45 - 6x < 18? 

7.3 Solving Linear Systems by Addition or Sub- 
traction 

As you noticed in the previous lesson, solving a system algebraically will give you the most accurate answer 
and in some cases, it is easier than graphing. However, you also noticed that it took some work in several 
cases to rewrite one equation before you could use the Substitution Property. There is another method 
used to solve systems algebraically: the elimination method. 

The purpose of the elimination method to solve a system is to cancel, or eliminate, a variable by either 
adding or subtracting the two equations. This method works well if both equations are in standard form. 

Example 1: // one apple plus one banana costs $1.25 and one apple plus two bananas costs $2.00, how 
much does it cost for one banana? One apple? 

Solution: Begin by defining the variables of the situation. Let a = the number of apples and b = the 
number of bananas. By translating each purchase into an equation, you get the following system: 

(a + b = 1.25 
[a + 2b = 2.00 

You could rewrite the first equation and use the Substitution Property here, but because both equations 
are in standard form, you can also use the elimination method. 

Notice that each equation has the value la. If you were to subtract these equations, what would happen? 

a + b = 1.25 
-(^ + 2/7 = 2.00) 



- b = -0.75 
b = 0.75 

Therefore, one banana costs $0.75, or 75 cents. By subtracting the two equations, we were able to eliminate 
a variable and solve for the one remaining. 

How much is one apple? Use the first equation and the Substitution Property. 

a + 0.75 = 1.25 

a = 0.50 — > one apple costs 50 cents 



Example: Solve the system 



|3x+2y= 11 
[5;c-2y= 13 



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Solution: These equations would take much more work to rewrite in slope-intercept form to graph or to use 
the Substitution Property. This tells us to try to eliminate a variable. The coefficients of the x-variables 
have nothing in common, so adding will not cancel the x-variable. 

Looking at the y-variable, you can see the coefficients are 2 and -2. By adding these together, you get 
zero. Add these two equations and see what happens. 

3x + 2y = 11 

+ (5x - 2y) = 13 



8x + Oy = 24 



The resulting equation is 8x = 24. Solving for x, you get x = 3. To find the y-coordinate, choose either 
equation, and substitute the number 3 for the variable x. 

3(3) + 2v = ll 
9 + 2y = ll 
2y = 2 
y = l 

The point of intersection of these two equations is (3, 1). 




Dagwood2 1 /wwwilickncom/creativecoinmons 

Example: Andrew is paddling his canoe down a fast-moving river. Paddling downstream he travels at 7 
miles per hour, relative to the river bank. Paddling upstream, he moves slower, traveling at 1.5 miles per 
hour. If he paddles equally hard in both directions, calculate, in miles per hour, the speed of the river and 
the speed Andrew would travel in calm water. 

Solution: We have two unknowns to solve for, so we will call the speed that Andrew paddles at jc, and the 
speed of the river y. When traveling downstream, Andrew's speed is boosted by the river current, so his 
total speed is the canoe speed plus the speed of the river (x + y). Upstream, his speed is hindered by the 
speed of the river. His speed upstream is (x-y). 

Downstream Equation x + y = 7 

Upstream Equation x-y = 1.5 

Notice y and -y are additive inverses. If you add them together, their sum equals zero. Therefore, by adding 
the two equations together, the variable y will cancel, leaving you to solve for the remaining variable, x. 

x + y = 7 
+ (x-y) = 1.5 



2x + Oy = 8.5 
2x = 8.5 



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Therefore, x = 4.25; Andrew is paddling 4.25 miles /hour. To find the speed of the river, substitute your 
known value into either equation and solve. 

4.25 -y = 1.5 
-y = -2.75 
y = 2.75 

The stream's current is moving at a rate of 2.75 miles/hour. 

Multimedia Link: For more help with solving systems by elimination, visit this site: http://www. 
teachertube . com/viewVideo . php?t itle=Solving_System_of _Equat ions_using_Eliminat ion&#38 ; video_ 
id=10148 Teacher Tube video. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Linear Systems by Elimination (12:44) 




Figure 7.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/776 



1. What is the purpose of the elimination method to solve a system? When is this method appropriate? 



In 2 - 10, solve each system using elimination. 



2. 



3. 



6. 



2x + y = -17 
8x-3y = -19 
x + 4y = -9 
-2x - 5y = 12 
-2x-5y = -10 
x + 4y = 8 
x-3y = -10 
-8x + 5y = -15 
-x-6y = -18 
x - 6y = -6 



277 



www.ckl2.org 



7 J5x-3y = -14 
' \x-3y = 2 

8. 3;t + 4;y = 2.5 
5x - 4y = 25.5 

9. $x + 7y = -31 
5x-9y = 17 

10. 3y - 4x = -33 
5jc - 3y = 40.5 

11. Nadia and Peter visit the candy store. Nadia buys three candy bars and four fruit roll-ups for $2.84. 
Peter also buys three candy bars, but he can afford only one fruit roll-up. His purchase costs $1.79. 
What is the cost of each candy bar and each fruit roll-up? 

12. A small plane flies from Los Angeles to Denver with a tail wind (the wind blows in the same direction 
as the plane), and an air-traffic controller reads its ground-speed (speed measured relative to the 
ground) at 275 miles per hour. Another identical plane moving in the opposite direction has a 
ground-speed of 227 miles per hour. Assuming both planes are flying with identical air-speeds, 
calculate the speed of the wind. 

13. An airport taxi firm charges a pick-up fee, plus an additional per-mile fee for any rides taken. If a 
12-mile journey costs $14.29 and a 17-mile journey costs $19.91, calculate: 

(a) the pick-up fee 

(b) the per-mile rate 

(c) the cost of a seven-mile trip 

14. Calls from a call-box are charged per minute at one rate for the first five minutes, then a different 
rate for each additional minute. If a seven-minute call costs $4.25 and a 12-minute call costs $5.50, 
find each rate. 

15. A plumber and a builder were employed to fit a new bath, each working a different number of hours. 
The plumber earns $35 per hour, and the builder earns $28 per hour. Together they were paid 
$330.75, but the plumber earned $106.75 more than the builder. How many hours did each work? 

16. Paul has a part-time job selling computers at a local electronics store. He earns a fixed hourly wage, 
but he can earn a bonus by selling warranties for the computers he sells. He works 20 hours per 
week. In his first week, he sold eight warranties and earned $220. In his second week, he managed 
to sell 13 warranties and earned $280. What is Paul's hourly rate, and how much extra does he get 
for selling each warranty? 

Mixed Review 

17. Graph y = |x| - 5. 

18. Solve. Write the solution using interval notation and graph the solution on a number line: -9 > ^. 

19. The area of a rectangle is 1,440 square centimeters. Its length is ten times more than its width. 
What are the dimensions of the rectangle? 

20. Suppose f(x) = 8x 2 - 10. Find /(-6). 

21. Torrey is making candles from beeswax. Each taper candle needs 86 square inches and each pillar 
candle needs 264 square inches. Torrey has a total of 16 square feet of beeswax. Graph all the 
possible combinations of taper and pillar candles Torrey could make (Hint: one square foot = 
144 square inches). 

7.4 Solving Linear Systems by Multiplication 

This chapter has provided three methods to solve systems: graphing, substitution, and elimination through 
addition and subtraction. As stated in each lesson, these methods have strengths and weaknesses. Below 

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is a summary. 
Graphing 

y A good technique to visualize the equations and when both equations are in slope-intercept form. 

• Solving a system by graphing is often imprecise and will not provide exact solutions. 

Substitution 

/ Works particularly well when one equation is in standard form and the second equation is in slope- 
intercept form. 

/ Gives exact answers. 

• Can be difficult to use substitution when both equations are in standard form. 

Elimination by Addition or Subtraction 

y Works well when both equations are in standard form and the coefficients of one variable are additive 
inverses. 

y Answers will be exact. 

• Can be difficult to use if one equation is in standard form and the other is in slope-intercept form. 

• Addition or subtraction does not work if the coefficients of one variable are not additive inverses. 

Although elimination by only addition and subtraction does not work without additive inverses, you can 
use the Multiplication Property of Equality and the Distributive Property to create additive inverses. 

Multiplication Property and Distributive Property: 

// ax + by = c, then m(ax + by) = m(c) and m(ax + by) = m(c) — > (am)x + (bm)y = mc 

While this definition box may seem complicated, it really states you can multiply the entire equation by 
a particular value and then use the Distributive Property to simplify. The value you are multiplying is 
called a scalar. 

Example: Solve the system I 

[5x-2y=ll 

Solution: Neither variable has additive inverse coefficients. Therefore, simply adding or subtracting the 
two equations will not cancel either variable. However, there is a relationship between the coefficients of 
the y- variable. 

4 is the additive inverse of - 2 X (2) 



By multiplying the second equation by the scalar 2, you will create additive inverses of y. You can then 
add the equations. 

hx + 4y = 12 
[2(5x-2y = 11) "* 

Add the two equations. 
Divide by 17. 



7x + Ay = 


■■ 12 






10* - 


-Ay~- 


= 22 


17jc = 

x = 


:34 

= 2 



279 www.ckl2.org 



To find the y-value, use the Substitution Property in either equation. 



[2) + Ay = 


: 12 


14 + Ay = 


: 12 


Ay = 


-2 


y = 


1 
~2 



The solution to this system is (2, -|J. 

Example: Andrew and Anne both use the I-Haul truck rental company to move their belongings from home 
to the dorm rooms on the University of Chicago campus. I-Haul has a charge per day and an additional 
charge per mile. Andrew travels from San Diego, California, a distance of 2,060 miles in five days. Anne 
travels 880 miles from Norfolk, Virginia, and it takes her three days. If Anne pays $840 and Andrew pays 
$1,845.00, what does I-Haul charge: 

a) per day? 

b) per mile traveled? 

Solution: Begin by writing a system of linear equations: one to represent Anne and the second to represent 
Andrew. Let x = amount charged per day and y = amount charged per mile. 

fax + 880); = 840 
[5jc + 2060y = 1845 

There are no relationships seen between the coefficients of the variables. Instead of multiplying one equation 
by a scalar, we must multiply both equations by the least common multiple. 

The least common multiple is the smallest value that is divisible by two or more quantities without a 
remainder. 

Suppose we wanted to eliminate the variable x because the numbers are smaller to work with. The 
coefficients of x must be additive inverses of the least common multiple. 

LCM of 3 and 5 = 15 

J-5(3jc + 880y = 840) J- 15* - 4400y = -4200 

[3(5* + 2060y = 1845) "* [I5x + 6180y = 5535 

Adding the two equations yields: 1780y = 1335 

Divide byl780 y = 0.75 

The company charges $0.75 per mile. 

To find the amount charged per day, use the Substitution Property and either equation. 

5x + 2060(0.75) = 1845 
5* +1545 = 1845 
5x + 1545 - 1545 = 1845 - 1545 
5x = 300 
x = 60 

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I-Haul charges $60.00 per day and $0.75 per mile. 

Multimedia Link: For even more practice, we have this video. One common type of problem involving 
systems of equations (especially on standardized tests) is "age problems." In the following video, the 
narrator shows two examples of age problems, one involving a single person and one involving two people. 
Khan Academy Age Problems (7:13) 




Figure 7.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/452 

For more help with solving systems by eliminating a variable, visit this site: http: //www. bright storm, 
com/math/algebra/solving- systems- of -equations/solving- systems- of -equations-using- elimination 
- Brightstorm video. You may need to set up a free account with Brightstorm to finish watching the video. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Linear Systems by Multiplication (12:00) 




Figure 7.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/777 



Find the least common multiple of the values given. 



1. 
2. 
3. 

4. 

5. 
6. 



5 and 7 
-11 and 6 
15 and 8 
7 and 12 
2 and 17 
-3 and 6 



7. 6 and ^ 



281 



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8. 3 and 111 

9. 9 and 14 
10. 5 and -5 

List the scalar needed to create the additive inverse. 

11. multiply by 6 to create additive inverse of 12. 

12. multiply by 5 to create additive inverse of 35. 

13. multiply by -10 to create additive inverse of 80. 

14. multiply by -7 to create additive inverse of 63. 

15. What could you multiply 11 by to create the additive inverse of 121? 

16. What scalar could you multiply 4 by to create the additive inverse of -16? 

Solve the following systems using multiplication. 

17. 5x - lOv = 15 
3x - 2y = 3 

18. 5x-y = 10 
3x-2y = -1 

19. 5x + 7y= 15 
7x - 3 y = 5 

20. 9x + 5y = 9 
12x + 8y = 12.8 

21. 4x-3y= 1 
3x - 4y = 4 

22. 7x-3y = -3 
6jc + 4y = 3 

In 23 - 28, solve the systems using any method. 

23. x = 3y 

x - 2y = -3 

24. y = 3x + 2 

y = -2x + 7 

25. 5x-5y = 5 
5x + 5y = 35 

26. y = -3jc-3 

3x - 2y + 12 = 

27. 3jc - 4y = 3 
4y + 5x = 10 

28. 9jc - 2y = -4 
2x - 6y = 1 

29. Supplementary angles are two angles whose sum is 180°. Angles A and B are supplementary angles. 
The measure of Angle A is 18° less than twice the measure of Angle B. Find the measure of each 
angle. 

30. A farmer has fertilizer in 5% and 15% solutions. How much of each type should he mix to obtain 
100 liters of fertilizer in a 12% solution? 

31. A 150-yard pipe is cut to provide drainage for two fields. If the length of one piece is three yards less 
than twice the length of the second piece, what are the lengths of the two pieces? 

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4 


8 


12 


16 


20 


24 


28 


30 


2 


3.2 


4 


5.6 


7 


7.9 


8.6 


9.1 



32. Mr. Stein invested a total of $100,00 in two companies for a year. Company A's stock showed a 13% 
annual gain, while Company B showed a 3% loss for the year. Mr. Stein made an overall 8% return 
on his investment over the year. How much money did he invest in each company? 

33. A baker sells plain cakes for $7 or decorated cakes for $11. On a busy Saturday, the baker started 
with 120 cakes, and sold all but three. His takings for the day were $991. How many plain cakes did 
he sell that day, and how many were decorated before they were sold? 

34. Twice John's age plus five times Claire's age is 204. Nine times John's age minus three times Claire's 
age is also 204. How old are John and Claire? 

Mixed Review 

35. Baxter the golden retriever is lying in the sun. He casts a shadow of 3 feet. The doghouse he is next 
to is 3 feet tall and casts an 8-foot shadow. What is Baxter's height? 

36. A botanist watched the growth of a lily. At 3 weeks, the lily was 4 inches tall. Four weeks later, the 
lily was 21 inches tall. Assuming this relationship is linear: 

(a) Write an equation to show the grow pattern of this plant. 

(b) How tall was the lily at the 5. 5- week mark? 

(c) Is there a restriction on how high the plant will grow? Does your equation show this? 

37. The "Wave" is an exciting pasttime at football games. To prepare, students in a math class took the 
data in the table below. 

(a) Find a linear regression equation for this data. Use this model to estimate the number of seconds 
it will take for 18 students to complete a round of the wave. 

(b) Use the method on interpolation to determine the amount of time it would take 18 students to 

complete the wave, . x 

s (number oi students in wave) 

t (time in seconds to complete on full round) 

Quick Quiz 

f-3j = 3x + 6 

;em < 

(3; = 6x+17 

2. Solve the system: < 

\y = 7x + 20 

3. Joann and Phyllis each improved their flower gardens by planting daisies and carnations. Joann 
bought 10 daisies and 4 carnations and paid $52.66. Phyllis bought 3 daisies and 6 carnations and 
paid $43.11 How much is each daisy? How much is each carnation? 

4. Terry's Rental charges $49 per day and $0.15 per mile to rent a car. Hurry-It-Up charges a flat fee of 
$84 per day to rent a car. Write these two companies' charges in equation form and use the system 
to determine at what mileage the two companies will charge the same for a one-day rental. 

7.5 Special Types of Linear Systems 

Solutions to a system can have several forms: 

• One intersection 

• Two or more solutions 

• No solutions 

• An infinite amount of solutions 

283 www.ckl2.org 



1. Is (-3, -5) a solution to the system 

V ; ly = -3x + 4 



Inconsistent Systems 



This lesson will focus on the last two situations: systems with no solutions or systems with an infinite 
amount of solutions. 

A system with parallel lines will have no solutions. 

Remember from chapter 5 that parallel lines have the same slope. When graphed, the lines will have the 
same steepness with different y-intercepts. Therefore, parallel lines will never intersect, thus they have no 
solution. 




x 
Algebraically, a system with no solutions looks like this when solved. 

Uy = 5- 3x 

J6x + 8y = 7 

The first equation in this system is "almost" solved for y. Substitution would be appropriate to solve this 
system. 

Uy = 5 - 3x ^ (y = f - \x 

\Qx + 8y = 7 ^ [6x + 8y = 7 

Using the Substitution Property, replace the y— variable in the second equation with its algebraic expression 
in equation #1. 

Apply the Distributive Property. 6x + 10 - Qx = 7 

Add like terms. 10 = 7 

You have solved the equation correctly, yet the answer does not make sense. 

When solving a system of parallel lines, the final equation will be untrue. 

Because 10 ^ 7 and you have done your math correctly, you can say this system has "no solutions." 

A system with no solutions is called an inconsistent system. 

Consistent Systems 

Consistent systems, on the contrary, have at least one solution. This means there is at least one 
intersection of the lines. There are three cases for consistent systems: 

• One intersection, as you have practiced the majority of this chapter 
www.ckl2.org 284 



Two or more intersections, as you will see when a quadratic equation intersects a linear equation 
Infinitely many intersections, as with coincident lines 




x 

Coincident lines are lines with the same slope and y-intercept. The lines completely overlap. 
When solving a consistent system involving coincident lines, the solution has the following result. 




, , i n , \-3(x + y = 3) \-3x-3y = -9 

Multiply the first equation by -3: < — > < 

[3x + 3y = 9 [3x + 3y = 9 

Add the equations together. 

= 

There are no variables left and you KNOW you did the math correctly. However, this is a true statement. 

When solving a system of coincident lines, the resulting equation will be without variables and the statement 
will be true. You can conclude the system has an infinite number of solutions. This is called a 
consistent-dependent system. 

Example 1: Identify the system as consistent, inconsistent, or consistent- dependent. 

3x-2y = 4 
9x-6y=l 

Solution: Because both equations are in standard form, elimination is the best method to solve this 
system. 

Multiply the first equation by 3. 

3(3x-2y = 4) 9x - 6y = 12 

=> 
9x - 6y = 1 9x - 6y = 1 

285 www.ckl2.org 



Subtract the two equations. 

9x-6y = 12 
9x - 6y = 1 

= 11 This Statement is not true. 
This is an untrue statement; therefore, you can conclude: 

1. These lines are parallel. 

2. The system has no solution. 

3. The system is inconsistent. 

Example 2: Two movie rental stores are in competition. Movie House charges an annual membership of 
$30 and charges $3 per movie rental. Flicks for Cheap charges an annual membership of $15 and charges 
$3 per movie rental. After how many movie rentals would Movie House become the better option? 

Solution: It should already be clear to see that Movie House will never become the better option, since its 
membership is more expensive and it charges the same amount per move as Flicks for Cheap. 

The lines that describe each option have different y-intercepts, namely 30 for Movie House and 15 for 
Flicks for Cheap. They have the same slope, three dollars per movie. This means that the lines are parallel 
and the system is inconsistent. 

Let's see how this works algebraically. 

Define the variables: Let x = number of movies rented and y = total rental cost 

(y = 30 + 3x 
\y = 15 + 3x 

Because both equations are in slope-intercept form, solve this system by substituting the second equation 
into the first equation. 

15 + 3x = 30 + 3x => 15 = 30 
This statement is always false. Therefore, the system is inconsistent with no solutions. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Special Types of Linear Systems (15:18) 

1. Define an inconsistent system. What is true about these systems? 

2. What are the three types of consistent systems? 

3. You graph a system and see only one line. What can you conclude? 

4. You graph a system and see the lines have an intersection point. What can you conclude? 

5. The lines you graphed appear parallel. How can you verify the system will have no solution? 

www.ckl2.org 286 




Figure 7.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/778 



6. You graph a system and obtain the following graph. Is the system consistent or inconsistent? How 
many solutions does the system have? 



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In 7 - 24, find the solution of each system of equations using the method of your choice. Please state 
whether the system is inconsistent, consistent, or consistent-dependent. 



7. 3jc - 4y = 13 
y = -3x - 7 

8. 4x + y = 3 
12jc + 3y = 9 

9. 10x-3y = 3 
2x + y = 9 

10. 2x-5y = 2 
4x + y = 5 



11. 



3a- 



5 +? = 3 

1.2* + 2j = 6 

12. 3x - Ay = 13 
j = -3x - 7 

13. 3x - 3>> = 3 
x-y = 1 

14. 0.5x-;y = 30 
0.5x-)> = -30 

15. 4x - 2y = -2 
3x + 2y = -12 



287 



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16. 3;t + 2;y = 4 

- 2x + 2y = 24 

17. 5;t-2;y = 3 
2x - 3y = 10 

18. 3x-4y= 13 
y = -3x-y 

19. 5jt-4y = 1 

- 10* + 8y = -30 

20. 4;t + 5y = 
3* = 6y + 4.5 

21. -2y + 4x = 8 
y - 2x = -4 

22. x - 2 = 2 
3x + y = 6 

23. 0.05jc + 0.25y = 6 

X + y = 24 

24. x+f = 6 
3x + 2y = 2 

25. Peter buys two apples and three bananas for $4. Nadia buys four apples and six bananas for $8 from 
the same store. How much does one banana and one apple costs? 

26. A movie rental store, CineStar, offers customers two choices. Customers can pay a yearly membership 
of $45 and then rent each movie for $2, or they can choose not to pay the membership fee and rent 
each movie for $3.50. How many movies would you have to rent before membership becomes the 
cheaper option? 

27. A movie house charges $4.50 for children and $8.00 for adults. On a certain day, 1200 people enter 
the movie house and $8,375 is collected. How many children and how many adults attended? 

28. Andrew placed two orders with an internet clothing store. The first order was for 13 ties and four 
pairs of suspenders, and it totaled $487. The second order was for six ties and two pairs of suspenders, 
and it totaled $232. The bill does not list the per-item price but all ties have the same price and all 
suspenders have the same price. What is the cost of one tie and of one pair of suspenders? 

29. An airplane took four hours to fly 2400 miles in the direction of the jet-stream. The return trip against 
the jet-stream took five hours. What were the airplane's speed in still air and the jet-stream's speed? 

30. Nadia told Peter that she went to the farmer's market, that she bought two apples and one banana, 
and that it cost her $2.50. She thought that Peter might like some fruit so she went back to the seller 
and bought four more apples and two more bananas. Peter thanked Nadia, but he told her that he 
did not like bananas, so he would pay her for only four apples. Nadia told him that the second time 
she paid $6.00 for the fruit. Please help Peter figure out how much to pay Nadia for four apples. 



Mixed Review 



31. A football stadium sells regular and box seating. There are twelve times as many regular seats as 
there are box seats. The total capacity of the stadium is 10,413. How many box seats are in the 
stadium? How many regular seats? 

32. Find an equation for the line perpendicular to y = — |jc - 8.5 containing the point (2, 7). 

33. Rewrite in standard form: y = ~x - 4. 

34. Find the sum: 7§ + |. 

35. Divide |*-§. 

36. Is the product of two rational numbers always a rational number? Explain your answer. 

www.ckl2.org 288 



7.6 Systems of Linear Inequalities 

The chapter moves on to the concept of systems of linear inequalities. In the last chapter, you learned how 
to graph a linear inequality in two variables. 

Step 1: Graph the equation using the most appropriate method. 



Slope-intercept form uses the y-intercept and slope to find the line. 
Standard form uses the intercepts to graph the line. 
Point-slope uses a point and the slope to graph the line. 



Step 2: If the equal sign is not included draw a dashed line. Draw a solid line if the equal sign is included. 

Step 3: Shade the half plane above the line if the inequality is "greater than." Shade the half plane under 
the line if the inequality is "less than." 

In this section, we will learn how to graph two or more linear inequalities on the same coordinate plane. The 
inequalities are graphed separately on the same graph and the solution for the system of inequalities 

is the common shaded region between all the inequalities in the system. 

The common shaded region of the system of inequalities is called the feasible region. 



fox + 3y < 18 



Example: Solve the system of inequalities 

I x - 4y < 12 

Solution: The first equation is written in standard form and can be graphed using its intercepts. The line 
is solid because the equal sign is included in the inequality. Since the inequality is less than or equal to, 
shade the half plane below the line. 




yi--|x + i 



The second equation is a little tricky. Rewrite this in slope-intercept form to graph. 



< 4y < -x + 12 



y>--3 



The division by -4 causes the inequality to reverse. The line is solid again because the equal sign is included 
in the inequality. Shade the half plane above the boundary line because y is greater than or equal. 



289 



www.ckl2.org 



y>f-3 




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When we combine the graphs, we see that the blue and red shaded regions overlap. This overlap is where 
both inequalities work. Thus the purple region denotes the solution of the system, the feasible region. 



■■■■■■■■■■■ 



4 6J^KT\2 r x 



The kind of solution displayed in this example is called unbounded, because it continues forever in at 
least one direction (in this case, forever upward and to the left). 

Bounded regions occur when more than two inequalities are graphed on the same coordinate plane, as in 
the next example. 

Example: Find the solution set to the following system. 



y > 3x - 4 

9 

y <--x + 2 
4 

x>0 
y>0 



Solution: Graph each line and shade appropriately. 
www.ckl2.org 290 




y > 3x - 4 




y <--x + 2 
Finally we graph and x > and y > 0, and the intersecting region is shown in the following figure. 































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Writing Systems of Linear Inequalities 

In some cases, you are given the feasible region and asked to write the system of inequalities. To do this, 
you work in reverse order of graphing. 

• Write the equation for the boundary line. 



291 



www.ckl2.org 



• Determine whether the sign should include "or equal to." 

• Determine which half plane is shaded. 

• Repeat for each boundary line in the feasible region. 

Example: Write the system of inequalities shown below. 




There are two boundary lines, so there are two inequalities. Write each one in slope-intercept form. 

y<\x + 7 

5 c 

Multimedia Link: For more help with graphing systems of inequalities and how to use your graphing 
calculator to graph a system of inequalities, visit the CK-12 Basic Algebra: 33 Graph System of Inequalities 
- Teacher Tube video or this video by CK-12 Basic Algebra: Graphing Systems of Linear Inequalities. - 




Figure 7.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/779 



Gdawgenterprises. 



Linear Programming — Real- World Systems of Linear Inequalities 

Entire careers are devoted to using systems of inequalities to ensure a company is making the most profit 
by producing the right combination of items or is spending the least amount of money to make certain 
items. Linear programming is the mathematical process of analyzing a system of inequalities to make 
the best decisions given the constraints of the situation. 

Constraints are the particular restrictions of a situation due to time, money, or materials. 
www.ckl2.org 292 




Figure 7.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/780 



The goal is to locate the feasible region of the system and use it to answer a profitability, or optimization, 
question. 

Theorem: The maximum or minimum values of an optimization equation occur at the vertices of the 
feasible region - at the points where the boundary lines intersect. 

This theorem provides an important piece of information. While the individual colors of the inequalities 
will overlap, providing an infinite number of possible combinations, only the vertices will provide the 
maximum (or minimum) solutions to the optimization equation. 

Let's go back to the situation presented in the chapter opener. 

James is trying to expand his pastry business to include cupcakes and personal cakes. He has 40 hours 
available to decorate the new items and can use no more than 22 pounds of cake mix. Each personal cake 
requires 2 pounds of cake mix and 2 hours to decorate. Each cupcake order requires one pound of cake mix 
and 4 hours to decorate. If he can sell each personal cake for $14.99 and each cupcake order for $16.99, 
how many personal cakes and cupcake orders should James make to make the most revenue? 

There are four inequalities in this situation. First, state the variables. Let p = the number of personal 
cakes and c = the number of cupcake orders. 

Translate this into a system of inequalities. 

2p + lc < 22 - This is the amount of available cake mix. 

2p + 4c < 40 - This is the available time to decorate. 

p > - You cannot make negative personal cakes. 

c > - You cannot make negative cupcake orders. 

Now graph each inequality and determine the feasible region. 



293 



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,: 



The feasible region has four vertices {(0, 0),(0, 10), (11, 0),(8, 6)}. According to our theorem, the opti- 
mization answer will only occur at one of these vertices. 

Write the optimization equation: How much of each type of order should James make to bring in the most 
revenue? 

14.99/? + 16.99c = maximum revenue 

Substitute each ordered pair to determine which makes the most money 

(0,0) -^$0.00 
(0, 10) -> 14.99(0) + 16.99(10) = $169.90 
(11,0) -> 14.99(11) + 16.99(0) = $164.89 

(8,6) -> 14.99(8) + 16.99(6) = $221.86 

To make the most revenue, James should make 8 personal cakes and 6 cupcake orders. 

For more help with applying systems of linear inequalities, watch this video by http://www.phscb.ool. 
com/atschool/academyl23/english/academyl23_content/wl-book-demo/ph-240s .html - PH School. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Systems of Linear Inequalities (8:52) 



1. What is linear programming! 

2. What is the feasible region of a system of inequalities? 

3. How do constraints affect the feasible region? 

4. What is an optimization equation? What is its purpose? 



www.ckl2.org 



294 




Figure 7.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/781 

5. You have graphed a feasible region. Where are the maximum (or minimum) points of the optimization 
equation located? 

Find the solution region of the following systems of inequalities. 



6. 4y-5x<8 

- 5x > 16 - 8y 

7. 5x - v > 5 
2y - x > -10 

8. 2x-3v<21 
x + 4 y < 6 
3x + y > -4 

y>±x-3 



9. 



10. 



11. 



12. 



13. 



(y < f x + 8 
\y < \x - 5 
[y > -2x + 2 
[y > -x + 1 
|y>±x + 6 
Jy>-±x + 4 
|x<-4 
fy<6 
[y>±x + 6 



Write the system of inequalities for each feasible region pictured below. 



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295 



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15. 




2 x 



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Given the following constraints find the maximum and minimum values for: 



17. z = -x + 5y 
x + 3y < 
x-y > 

3x - 7y < 16 

18. Find the maximum and minimum value of z 



= 2x + 5y azi'en the constraints. 
2x-y<12 



4x + 3y > 
x -y < 6 

19. In Andrew's Furniture Shop, he assembles both bookcases and TV cabinets. Each type of furniture 
takes him about the same time to assemble. He figures he has time to make at most 18 pieces of 
furniture by this Saturday. The materials for each bookcase cost him $20.00 and the materials for 
each TV stand cost him $45.00. He has $600.00 to spend on materials. Andrew makes a profit of 
$60.00 on each bookcase and a profit of $100.00 for each TV stand. Find how many of each piece of 
furniture Andrew should make so that he maximizes his profit. 

20. You have $10,000 to invest, and three different funds from which to choose. The municipal bond fund 
has a 5% return, the local bank's CDs have a 7% return, and a high-risk account has an expected 10% 
return. To minimize risk, you decide not to invest any more than $1,000 in the high-risk account. 
For tax reasons, you need to invest at least three times as much in the municipal bonds as in the 
bank CDs. Assuming the year-end yields are as expected, what are the optimal investment amounts? 

Mixed Review 



www.ckl2.org 



296 



12jK + 8y = 24 

21. Solve by elimination < 

[-6x + 3y = 9 

22. Solve 36 = |5f-6|. 

23. Determine the intercepts of y = -|x - 3. 

24. Jerry's aunt repairs upholstery. For three hours' worth of work, she charges $145. For nine hours 
of work, she charges $355. Assuming this relationship is linear, write the equation for this line in 
point-slope form. How much would Jerry's aunt charge for 1.25 hours worth of work? 

25. Translate into an algebraic sentence: "Yoder is four years younger than Kate. Kate is six years 
younger than Dylan. Dylan is 20." How old is each person? 

7.7 Probability and Permutations 

Congratulations! You have won a free trip to Europe. On your trip you have the opportunity to visit 6 
different cities. You are responsible for planning your European vacation. How many different ways can 
you schedule your trip? The answer may surprise you! 




This is an example of a permutation. 

A permutation is an arrangement of objects in a specific order. It is the product of the counting numbers 
1 through n. 

n\ =n(n-l)(n-2) •...• 1 

How many ways can you visit the European cities? There are 6 choices for the first stop. Once you have 
visited this city, you cannot return so there are 5 choices for the second stop, and so on. 

6 • 5 • 4 • 3 • 2 • 1 = 720 

There are 720 different ways to plan your European vacation! 

A permutation of n objects arranged k at a time is expressed as n Pk. 

Example 1: Evaluate qPs. 

Solution: This equation asks, "How many ways can 6 objects be chosen 3 at a time?" 

297 www.ckl2.org 



There are 6 ways to choose the first object, 5 ways to choose the second object, and 4 ways to choose the 
third object. 

6-5-4 = 120 

There are 120 different ways 6 objects can be chosen 3 at a time. 

Example 1 can also be written using the formula for permutation: 6^3 = (q%v = ft = 6 • 5 • 4 = 120. 

Permutations and Graphing Calculators 

Most graphing calculators have the ability to calculate a permutation. 

Evaluate qPs using a graphing calculator. 

Type the first value of the permutation, the n. Choose the [MATH] button, directly below the [ALPHA] 
key. Move the cursor once to the left to see this screen: 

MATH HUM CPX Iflfl^ 

1 s rand 

fflnPr 

3:nCr 

4: ! 

5:randlntt 

6:randHorn( 

7s randBint 

Option #2 is the permutation option. Press [ENTER] and then the second value of the permutation, the 
value of k. Press [ENTER] to evaluate. 

6 nPr 3 

120 



Permutations and Probability 

The letters of the word HOSPITAL are arranged at random. How many different arrangements can be 
made? What is the probability that the last letter is a vowel? 

There are eight ways to choose the first letter, seven ways to choose the second, and so on. The total 
number of arrangements is 8!= 40,320. 

There are three vowels in HOSPITAL; therefore, there are three possibilities for the last letter. Once this 
letter is chosen, there are seven choices for the first letter, six for the second, and so on. 

7-6- 5 -4-3 -2- 1-3 = 15,120 

Probability, as you learned in a previous chapter, has the formula: 

number of ways to get success 



Probability {success) 



total number of possible outcomes 
There are 15,120 ways to get a vowel as the last letter; there are 40,320 total combinations. 

„n r . A 15,120 3 

Pilast letter is a vowel) = = - 

v ; 40,320 8 

Multimedia Link: For more help with permutations, visit the http://regentsprep.org/REgents/ 
math/ALGEBRA/APR2/LpermProb.htm - Algebra Lesson Page by Regents Prep. 

www.ckl2.org 298 



10 

11 

12 
13 



Practice Set 

1. Define permutation. 

In 2 - 19, evaluate each permutation. 

2. 7! 

3. 10! 

4. 1! 

5. 5! 

6. 9! 

7. 3! 

8. 4! + 4! 

9. 16! -5! 

98! 
96! 
ill 
2! 

301! 
300! 
81 
3! 

14. 2! + 9! 

15. nP 2 

16. 5^5 

17. 5^3 

18. i 5 Pio 

19. 60^59 

20. How many ways can 14 books be organized on a shelf? 

21. How many ways are there to choose 10 objects, four at a time? 

22. How many ways are there to choose 21 objects, 13 at a time? 

23. A running track has eight lanes. In how many ways can 8 athletes be arranged to start a race? 

24. Twelve horses run a race. 

(a) How many ways can first and second places be won? 

(b) How many ways will all the horses finish the race? 

25. Six actors are waiting to audition. How many ways can the director choose the audition schedule? 

26. Jerry, Kerry, Larry, and Mary are waiting at a bus stop. What is the probability that Mary will get 
on the bus first? 

27. How many permutations are there of the letters in the word "HEART"? 

28. How many permutations are there of the letters in the word "AMAZING"? 

29. Suppose I am planning to get a three-scoop ice cream cone with chocolate, vanilla, and Superman. 
How many ice cream cones are possible? If I ask the server to "surprise me," what is the probability 
that the Superman scoop will be on top? 

30. What is the probability you choose two cards (without replacement) from a standard 52-card deck 
and both cards are jacks? 

31. The Super Bowl Committee has applications from 9 towns to host the next two Super Bowls. How 
many ways can they select the host if: 

(a) The town cannot host a Super Bowl two consecutive years? 

(b) The town can host a Super Bowl two consecutive years? 

Mixed Review 

32. Graph the solution to the following system: 

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2x - 3y > -9 
y<l 

33. Convert 24 meters/minute to feet/second. 

34. Solve for t: \t - 6| < -14. 

35. Find the distance between 6.15 and -9.86. 

36. Which of the following vertices provides the minimum cost according to the equation 12x + 20y = 
cost: (3, 6), (9,0), (6, 2), (0,11)? 

37. Write the system of inequalities pictured below. 

7.8 Probability and Combinations 

When the order of objects is not important and/or the objects are replaced, combinations are formed. 

A combination is an arrangement of objects in no particular order. 

Consider a sandwich with salami, ham, and turkey. It does not matter the order in which we place the 
deli meat, as long as it's on the sandwich. 

There is only one way to stack the meat on the sandwich if the order does not matter. However, if the order 
mattered, there are 3 choices for the first meat, 2 for the second, and one for the last choice: 3*2-1 = 6. 




Combination ^ Permutation 
A combination of n objects chosen k at a time is expressed as n Ck- 

This is read "n choose kT 

Example 1: How many ways can 8 students be chosen from a class of 21? 

Solution: It does not matter how the eight students are chosen. Use the formula for combination rather 
than permutation. 

21! 



8!(21 



= 203,490 



There are 203,490 different ways to choose eight students from 21. 

Example: The Senate is made of 100 people, two per state. How many different four-person committees 
are possible? 

Solution: This question does not care how the committee members are chosen; we will use the formula for 
combination. 

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100\ 100! 

4 J" 4!(l0034JT -".Ml.™-"*, 

That is a lot of possibilities! 

Combinations on the Graphing Calculator 

Just like permutations, most graphing calculators have the capability to calculate combinations. On the 
TI calculators, use these directions. 

• Enter the ft, or the total to choose from. 

• Choose the [MATH] button, directly below the [ALPHA] key. Move the cursor once to the left to 
see this screen: 

MATH HUM CPX Iflfl^ 

1 s rand 

fflnPr 

3:nCr 

4: ! 

5:randlntt 

6:randHorn( 

7s randBint 

• Choose option #3, n C r . Type in the k value, the amount you want to choose. 

100 nCr 4 

3921225 

Probability and Combinations 

Combinations are used in probability when there is a replacement of objects or the order does not matter. 

Suppose you have ten marbles: four blue and six red. You choose three marbles without looking. What is 
the probability that all three marbles are blue? 

_ number of ways to get success 

Probability [success) — 



total number of possible outcomes 
There are 4C3 ways to choose the blue marbles. There are 10C3 total combinations. 

(3) 4 1 

P(all 3 marbles are blue) = — — = — — = — 
There is approximately 3.33% chance of all three marbles being drawn are blue. 

Practice Set 

1. What is a combination! How is it different from a permutation? 

301 www.ckl2.org 



2. How many ways can you choose k objects from n possibilities? 

3. Why is 3C9 impossible to evaluate? 

In 4 - 19, evaluate the combination. 

<■ (?) 

«■(?) 

MS) 

8-0 

»-G) 

11. (I?) 

12. ® 

13. (?) 

14. 7C3 

15. 11C5 

16. 5C4 

17. 13C9 

18. 20C5 

19. 15C15 

20. Your backpack contains 6 books. You select two at random. How many different pairs of books could 
you select? 

21. Seven people go out for dinner. In how many ways can 4 order steak, 2 order vegan, and 1 order 
seafood? 

22. A pizza parlor has 10 toppings to choose from. How many four-topping pizzas can be created? 

23. Gooies Ice Cream Parlor offers 28 different ice creams. How many two-scooped cones are possible, 
given the order does not matter? 

24. A college football team plays 14 games. In how many ways can the season end with 8 wins, 4 losses, 
and 2 ties? 

25. Using the marble situation from the lesson, determine the probability that the three marbles chosen 
are all red? 

26. Using the marble situation from the lesson, determine the probability that two marbles are red and 
the third is blue. 

27. Using the Senate situation from the lesson, how many two-person committees can be made using 
Senators? 

28. Your English exam has seven essays and you must answer four. How many combinations can be 
made? 

29. The sociology test has 15 true/false questions. In how many ways can you answer 11 correctly? 

30. Seven people are applying for two vacant school board positions; four are women, three are men. In 
how many ways can these vacancies be filled ... 

(a) With any two applicants? 

(b) With only women? 

(c) With one man and one woman? 

Mixed Review 

31. How many ways can 15 paintings be lined along a wall? 
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32. Your calculator gives an "Overload" error when trying to simplify |^f. What can you do to help 
evaluate this fraction? 

33. Consider a standard six-sided die. What is the probability that the number rolled will be a multiple 
of 2? 

34. Solve the following system: The sum of two numbers is 70.6 and their product is 1,055.65. Find the 
two numbers. 



7.9 Chapter 7 Review 



1. Match the following terms to their definitions. 

(a) System - Restrictions imposed by time, materials, or money 

(b) Feasible Region - A system with an infinite amount of solutions 

(c) Inconsistent System - An arrangement of objects when order matters 

(d) Constraints - A method used by businesses to determine the most profitable or least cost given 
constraints 

(e) Consistent-dependent System - An arrangement of objects in which order does not matter 

(f) Permutation - Two or more algebraic sentences joined by the word and 

(g) Combination - A system with no solutions 

(h) Linear programming - A solution set to a system of inequalities 

2. Where are the solutions to a system located? 

3. Suppose one equation of a system is in slope-intercept form and the other is in standard form. Which 
method presented in this chapter would be the most effective to solve this system? Why? 

(7x-4y = ll 

4. Is (-3, -8) a solution to < ? 

|* + 2y = -19 

(y = 

5. Is (-1, 0) a solution to < ? 

(8x + 7y = 8 

Solve the following systems by graphing. 

6. 

7. 




10. 



Solve the following system by substitution. 




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12. 
13. 
14. 
15. 
16. 
17. 
18. 

Solve 

19. 
20. 
21. 

22. 
23. 

24. 
25. 
26. 
27. 
28. 



y = -3x + 22 
y = -2x + 16 
y = 3 - ^x 
x + 3y = 4 
2x + y = -10 
y = x + 14 
y + 19 = -7x 
y = -2x - 9 
y = 
5x = 15 
y = 3 - |x 
x + 3y = 4 
7x + 3y = 3 
y = 8 

the following systems using elimination. 

2x + 4y = -14 
-2x + 4y = 8 
6x - 9y = 27 
6jc - 8y = 24 
3x - 2y = 
2y - 3x = 
4x + 3y = 2 
-8jc + 3y = 14 
-8jc + 8y = 8 
6x + y = 1 
7jc-4);= 11 
x + 2y = -19 
y = -2x - 1 
4x + 6y = 10 
x - 6;y = 20 
2;y-3x = -12 
-4x + 4y = 
8x - 8y = 
-9jc + 6y = -27 
-3jc + 2y = -9 



Graph the solution set to each system of inequalities. 



3. 

I v ^ — 

29 

\y> -2x + 2 



|y>-5*-5 



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30. 



31. 



32. 



33. 



U>fx + ; 



[y * i x ■ 
\y<h 



\y > -2x + 
[y<-lx-. 



I y > | x + 4 



4. 

U < 5 

9. 

5' 



U>t* 



-2 



Write a system of inequalities for the regions below. 



34. 






35. 




36. Yolanda is looking for a new cell phone plan. Plan A charges $39.99 monthly for talking and $0.08 
per text. Plan B charges $69.99 per month for an "everything" plan. 

(a) At how many texts will these two plans charge the same? 

(b) What advice would you give Yolanda? 

37. The difference of two numbers is -21.3. Their product is -72.9. What are the numbers? 

38. Yummy Pie Company sells two kinds of pies: apple and blueberry. Nine apples pies and 6 blueberry 
pies cost $126.00. 12 apples pies and 12 blueberry pies cost $204.00. What is the cost of one apple 
pie and 2 blueberry pies? 

39. A jet traveled 784 miles. The trip took seven hours, traveling with the wind. The trip back took 14 
hours, against the wind. Find the speed of the jet and the wind speed. 

40. A canoe traveling downstream takes one hour to travel 7 miles. On the return trip, traveling against 
current, the same trip took 10.5 hours. What is the speed of the canoe? What is the speed of the 



305 



www.ckl2.org 



river : 

41. The yearly musical production is selling two types of tickets: adult and student. On Saturday, 120 
student tickets and 45 adult tickets were sold, bringing in $1,102.50 in revenue. On Sunday, 35 
student tickets and 80 adult tickets were sold, bringing in $890.00 in revenue. How much was each 
type of ticket? 

42. Rihanna makes two types of jewelry: bracelets and necklaces. Each bracelet requires 36 beads and 
takes 1 hour to make. Each necklace requires 80 beads and takes 3 hours to make. Rihanna only has 
600 beads and 20 hours of time. 1. Write the constraints of this situation as a system of inequalities. 

2. Graph the feasible region and locate its vertices. 

3. Rihanna makes $8.00 profit per bracelet and $7.00 profit per necklace. How many of each should 
she make to maximize her profit? 

43. A farmer plans to plant two type of crops: soybeans and wheat. He has 65 acres of available land. 
He wants to plant twice as much soybeans as wheat. Wheat costs $30 per acre and soybeans cost 
$30 per acre. 1. Write the constraints as a system of inequalities. 

2. Graph the feasible region and locate its vertices. 

3. How many acres of each crop should the farmer plant in order to minimize cost? 

44. How many ways can you organize 10 items on a shelf? 

45. Evaluate 5! 

46. Simplify ^ 

47. How many ways can a football team of 9 be arranged if the kicker must be in the middle? 

48. How many one-person committees can be formed from a total team of 15? 

49. How many three-person committees can be formed from a total team of 15? 

50. There are six relay teams running a race. How many different combinations of first and second place 
are there? 

51. How many ways can all six relay teams finish the race? 

52. Evaluate (^). 

53. Evaluate LJ and explain its meaning. 

54. A baked potato bar has 9 different choices. How many potatoes can be made with four toppings? 

55. A bag contains six green marbles and five white marbles. Suppose you choose two without looking. 
What is the probability that both marbles will be green? 

56. A principal wants to make a committee of four teachers and six students. If there are 22 teachers 
and 200 students, how many different committees can be formed? 

7.10 Chapter 7 Test 

1. True or false? A shorter way to write a permutation is m. 

(v = — x + 18 
17 91 ? 

3. What is the primary difference between a combination and a permutation? 

4. An airplane is traveling a distance of 1,150 miles. Traveling against the wind, the trip takes 12.5 
hours. Traveling with the wind, the same trip takes 11 hours. What is the speed of the plane? What 
is the speed of the wind? 

5. A solution set to a system of inequalities has two dashed boundary lines. What can you conclude 
about the coordinates on the boundaries? 

( 5x + 2y = 20 

6. What does k have to be to create a dependent-consistent system? < 

[15x + ky = 60 

7. Joy Lynn makes two different types of spring flower arrangements. The Mother's Day arrangement 
has 8 roses and 6 lilies. The Graduation arrangement has 4 roses and 12 lilies. Joy Lynn can use 

www.ckl2.org 306 



no more than 120 roses and 162 lilies. If each Mother's Day arrangement costs $32.99 and each 
Graduation arrangement costs $27.99, how many of each type of arrangement should Joy Lynn make 
to make the most revenue? 

f-6x + y = -1 

8. Solve the system < 

{-7x - 2y = 2 

|y = 

9. Solve the system< 

j&c + 7y = 8 

10. Solve [ y = X + 8 . 

\y = 3x + 16 

( y = -2x - 2 

11. How many solutions does the following system have? < 

\y = -2x + 17 

12. The letters to the word VIOLENT are placed into a bag. 

(a) How many different ways can all the letters be pulled from the bag? 

(b) What is the probability that the last letter will be a consonant? 

13. Suppose an ice cream shop has 12 different topping choices for an ice cream sundae. How many ways 
can you choose 5 of the 12 toppings? 

14. A saleswoman must visit 13 cities exactly once without repeating. In how many ways can this be 
done? 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/ 'flexr /chapter/ 96 17. 



307 www.ckl2.org 



Chapter 8 

Exponents and Exponential 
Functions 



Exponential functions occur in daily situations; money in a bank account, population growth, the decay of 
carbon- 14 in living organisms, and even a bouncing ball. Exponential equations involve exponents, or the 
concept of repeated multiplication. This chapter focuses on combining expressions using the properties of 
exponents. The latter part of this chapter focuses on creating exponential equations and using the models 
to predict. 




8.1 Exponential Properties Involving Products 

In this lesson, you will be learning what an exponent is and about the properties and rules of exponents. 
You will also learn how to use exponents in problem solving. 

Definition: An exponent is a power of a number that shows how many times that number is multiplied 
by itself. 

An example would be 2 3 . You would multiply 2 by itself 3 times, 2x2x2. The number 2 is the base and 
the number 3 is the exponent. The value 2 3 is called the power. 

Example 1: Write in exponential form: a xa xa xa. 

Solution: You must count the number of times the base, a, is being multiplied by itself. It's being 
multiplied four times so the solution is a 4 . 

Note: There are specific rules you must remember when taking powers of negative numbers. 



www.ckl2.org 308 



(negative number) X (positive number) = negative number 
(negative number) x (negative number) = positive number 

For even powers of negative numbers, the answer will always be positive. Pairs can be made with each 
number and the negatives will be cancelled out. 

(-2) 4 = (-2) (-2) (-2) (-2) = (-2)(-2) • (-2)(-2) = +16 

For odd powers of negative numbers, the answer is always negative. Pairs can be made but there will 
still be one negative number unpaired, making the answer negative. 

(_ 2 )5 = ( _ 2 )(_2)(-2)(-2)(-2) = (-2)(-2) • (-2)(-2) • (-2) = -32 

When we multiply the same numbers, each with different powers, it is easier to combine them before 
solving. This is why we use the Product of Powers Property. 

Product of Powers Property: For all real numbers x*X n ' X m = x n ~^ m - 

Example 2: Multiply x 4 ' X* • 

Solution: X ^ X ^= X ^= X Q 

Note that when you use the product rule you DO NOT MULTIPLY BASES. 

Example: 2 2 • 2 3 gfc 4 5 

Another note is that this rule APPLIES ONLY TO TERMS THAT HAVE THE SAME BASE. 

Example: 2 2 • 3 3 * 6 5 

(x 4 ) 3 = x 4 • x 4 - x 4 3 factors of x to the power 4. 

I A ' A ' A ' A I * I A ' A ' A ' A I * I A ' A ' A ' A I — lA'A'A'A'A'A'A'A'A'A'A'AI 
X 4 X 4 

This situation is summarized below. 

Power of a Product Property: For all real numbers x-> 

(x n r=x n - m 

The Power of a Product Property is similar to the Distributive Property. Everything inside the parentheses 
must be taken to the power outside. For example, (x 2 y) 4 = (x 2 ) 4 • (y) 4 = x 8 y 4 . Watch how it works the 
long way. 

(jc • x • y) - (x • x • y) • (jc • x • y) • (jc • x • y) = (x-x-x-x-x-x-x-x-y-y-y-y) 

x 2 y x 2 y x 2 y x 2 y x 8 y4 

The Power of a Product Property does not work if you have a sum or difference inside the parenthesis. For 
example, (x + y) 2 ± X 2 + J 2 • Because it is an addition equation, it should look like (x + j)ix + j)- 

Example 3: Simplify (x 2 ) 3 . 

Solution: (x 2 ) 3 =^ 3 = X 6 

309 www.ckl2.org 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Exponent Properties Involving Products (14:00) 




Figure 8.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/782 



1. Consider a 5 . 1. What is the base? 

2. What is the exponent? 

3. What is the power? 

4. How can this power be written using repeated multiplication? 

Determine whether the answer will be positive or negative. You do not have to provide the answer. 

2. -(3 4 ) 

3. -8 2 

4. 10x(-4) 3 

5. What is the difference between -5 2 and (-5) 2 ? 

Write in exponential notation. 

6. 2-2 

7. (-3)(-3)(-3) 

8. y-yy-yy 

9. (3a) (3a) (3a) (3a) 

io. 4-4.4.4-4 

11. 3x • 3x • 3x 

12. (-2a) (-2a) (-2a) (-2a) 

13. 6 - 6 - 6 - X- x-y -y -y -y 

Find each number. 



14. 


l 10 


15. 


3 


16. 


7 3 


17. 


-6 2 


WW 


.ckl2.or 



310 



18. 


5 4 


19. 


3 4 -3 7 


20. 


2 6 -2 


21. 


(4 2 ) 3 


22. 


(-2) 6 


23. 


(o-i) 5 


24. 


(-0.6) 3 



Multiply and simplify. 

25. 6 3 -6 6 

26. 2 2 • 2 4 • 2 6 

27. 3 2 -4 3 

28. x 2 

29. x 2 

30. (y 3 ) 5 

31. (-2y 4 )(-3y) 

32. (4a 2 )(-3a)(-5a 4 ) 

Simplify. 



x 4 
x 7 



33. 


a 3 ) 4 


34. 


>y) 2 


35. 


> 2 z> 3 ) 4 


36. 


-2xyV) 5 


37. 


;3x 2 y 3 ) • (4xy 2 ) 


38. 


;4xyz) • (x 2 y 3 ) • (2yz 4 


39. 


> 3 Z? 3 ) 2 


40. 


-8x) 3 (5x) 2 


41. 


> 2 )(-2a 3 ) 4 


42. 


I2xy)(12xy) 2 


43. 


;2xy 2 )(-x 2 y) 2 (3x 2 y 2 ; 


lixe< 


d Review 



44. How many ways can you choose a 4-person committee from seven people? 

45. Three canoes cross a finish line to earn medals. Is this an example of a permutation or a combination? 
How many ways are possible? 

46. Find the slope between (-9, 11) and (18, 6). 

47. Name the number set(s) to which V36 belongs. 

48. Simplify V74x2 \ 

49. 78 is 10% of what number? 

50. Write the equation for the line containing (5, 3) and (3, 1). 

8.2 Exponential Properties Involving Quotients 

In this lesson, you will learn how to simplify quotients of numbers and variables. 
Quotient of Powers Property: For all real numbers^, 4r = X n 



n—m 



311 www.ckl2.org 



When dividing expressions with the same base, keep the base and subtract the exponent in the denominator 
(bottom) from the exponent in the numerator (top). When we have problems with different bases, we apply 

7 

the rule separately for each base. To simplify ^, repeated multiplication can be used. 



.A- Jv'Jv'Jv'Jv'yL'yi/'yi' Jv ' Jv ' Jv 

X Ji * yV * yV * Ji -L 



.,3 



= X 



ry = ppp X . X y.J.y = x . x y =x 2 j0R *¥ = ^-3 3-2 = % 2 y 

x 3 y 2 }i • jk - ]t i • V 1 1 * x 3 y 2 

Example 1: Simplify each of the following expressions using the quotient rule. 



(a) 


X 5 






(b) 


X 3y2 






Solution: 




(a) 


x 10 
* 5 - 


-x 10 - 5 


-x 5 


(b) 


x 5 r 4 

X 3y2 


= x 5 ~ 3 


■J 4 -' 



4 ~ 2 -xV 



m) 






The power inside the parenthesis for the numerator and the denominator multiplies with the power outside 
the parenthesis. The situation below shows why this property is true. 

x 3 \ /jc 3 \ /x 3 \ /jc 3 \ /jc 3 \ (x - x - x) - (x - x - x) - (x- x - x) - (x - X- x) x 12 



\y 2 ) \y 2 ) \y 2 ) \y 2 ) \y 2 ) (yy)'(y'y)'(yy)'(y'y) y 8 

Example 2: Simplify the following expression. 
Solution: K? = C = X ^ 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Exponent Properties Involving Quotients (9:22) 

Evaluate the following expressions. 

1 h - 

2 Si 

o 3^ 
O. 34 

«■ at 

Simplify the following expressions. 

www.ckl2.org 312 




Figure 8.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/783 



5. 


a 3 

a 2 


6. 


X 5 




JO 


7. 


^ 


Jt* 


8. 


^ 
fl 


9. 


fl 5 £ 4 


fl 3 £ 2 


10. 


4 5 
42 


11. 


5 3 
5 7 


12. 


(S) 2 


13. 


/V6 4 \ 3 
\a 2 b ) 


14. 


x 6 y 5 
x 2 y 3 


15. 


6x 2 y s 
2xy 2 


16. 


(2a s b s \ 2 
\ 8a 7 b ) 


17. 


(* 2 ) 2 • £ 


18. 


/ 16a 2 \ 3 b 2 

U^ 5 / ' « 16 


19. 


6a 3 

2a 2 


20. 


15.x 5 
5x 


21. 


/18« 10 \ 4 
V 15a 4 / 


22. 


25yjc 6 




20y 5 ;c 2 


23. 




24. 


/6a 2 \ 2 5/7 
Ufc 4 / ' 3a 


25. 


(3^) 2 (4a 3 ^ 4 ) 3 


(6fl 2 /?) 4 


26. 


(2a 2 bc 2 )(6abc 3 ) 


4ab 2 c 



Mixed Review 



27. Evaluate x\z\ - \z\ when x = 8 and z = -4. 

(y < -x - 2 

28. Graph the solution set to the system < 

[y > -6jc + 3 

29. Evaluate g). 

30. Make up a situation that can be solved by 4! 

31. Write the following as an algebraic sentence: A number cubed is 8. 

313 



www.ckl2.org 



8.3 Zero, Negative, and Fractional Exponents 

In the previous lessons, we have dealt with powers that are positive whole numbers. In this lesson, you 
will learn how to solve expressions when the exponent is zero, negative, or a fractional number. 

Exponents of Zero: For all real numbers x*X ^ 0>Af° = 1- 

4 

Example: %-$ = x 4 ~ 4 = X° = 1- This example is simplified using the Quotient of Powers Property. 

Simplifying Expressions with Negative Exponents 

The next objective is negative exponents. When we use the quotient rule and we subtract a greater 
number from a smaller number, the answer will become negative. The variable and the power will be 
moved to the denominator of a fraction. You will learn how to write this in an expression. 

Example: ^ = x 4-6 = x~ 2 = -o . Another way to look at this is x ' x ' x ' x . The four vs on top will cancel 
out with four ^s on bottom. This will leave two ^s remaining on the bottom, which makes your answer 

look like -4. 

x 2 

Negative Power Rule for Exponents: \ = X~ n whereof ^ 

Example: x~ 6 7~ 2 — \ ' \ — ~r~2 • The negative power rule for exponents is applied to both variables 
separately in this example. 

Multimedia Link: For more help with these types of exponents, watch this http: //www.phschool . com/ 
atschool/academyl23/english/academyl23_content/wl-book-demo/ph-241s.html - PH School video 
or visit the http://www.mathsisfun.com/algebra/negative-exponents.html - mathisfun website. 

Example 1: Write the following expressions without fractions. 



(a) J, 




(b) £ 




Solution: 


(a)£ = 


= 2x" 2 


0>)£ = 


= x 2 y~ 3 



Notice in Example 1(a), the number 2 is in the numerator. This number is multiplied with^ 2 . It could 
also look like this, 2 • \ to be better understood. 



x* 



Simplifying Expressions with Fractional Exponents 

The next objective is to be able to use fractions as exponents in an expression. 
Roots as Fractional Exponents: i \[a" = a™ 
Example: ^[a = a^ , ifa = as, yep = (a 2 ) 5 = as = as 
Example 2: Simplify the following expressions. 

(a) W 

(b) ^ 
Solution: 



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It is important when evaluating expressions that you remember the Order of Operations. Evaluate what 
is inside the parentheses, then evaluate the exponents, then perform multiplication/division from left to 
right, then perform addition/subtraction from left to right. 

Example 3: Evaluate the following expression. 

(a) 3 • 5 2 - 10 • 5 + 1 

Solution: 3 • 5 2 - 10 • 5 + 1 = 3 • 25 - 10 • 5 + 1 = 75 - 50 + 1 = 26 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Zero, Negative, and Fractional Exponents (14:04) 




Figure 8.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/784 

Simplify the following expressions. Be sure the final answer includes only positive exponents. 



1. 


x~ l -y 2 


2. 


x- 4 


3. 


x- 3 

x~ r 


4. 


1 




X 


5. 


2 

.V 2 




2 


6. 


X 


7. 


_3_ 




xy 


8. 


3x" 3 


9. 


aW 1 


10. 


4x"V 


11. 


2x~ 2 

y-3 




1 1 


12. 


fl2 • as 


13. 


(alf 




5 


14. 


Cl2 

1 




a? 


15. 


(?)' 




— 3 —5 


16. 


x y 

„-7 



315 



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17. (x^y 3)(x 2 }73 N 

«. (f)" 2 

19. (3a-Vc 3 ) 3 

20. ;T 3 -;t 3 



Simplify the following expressions without any fractions in the answer. 

g- 3 (a 5 ) 





a" 6 


22. 


5xV 




X 8 J 


23. 


(4a6 6 ) 3 


(ab) 5 




I \ 3 


24. 


- 




W 


25. 


4a 2 b 3 
2a 5 b 


26. 


( x \ 3 * 2 y 
\3y 2 ) ' 4 


27. 


(I?) 2 


28. 


jc 3 ;y 2 
x 2 _y -2 


29. 


3jc 2 yi 
l 




xy 2 


30. 


(3x 3 )(4x 4 ) 


(2j) 2 


31. 


«- 2 r 3 
c- 1 




1 5 


39 


JC2y2 



Jt^)^ 



Evaluate the following expressions to a single number. 



33. 


3- 2 


34. 


(6.2)° 


35. 


8- 4 • 8 e 


36. 


(165) 3 


37. 


5° 


38. 
39. 


7 2 
(If 


40. 


3" 3 


41. 


165 


42. 


8^ 



In 43-45, evaluate the expression for x — 2,y — -l,z — 3. 

43. 2x 2 -3y 3 + 4z 

44. (x 2 -y 2 ) 2 

45. (^f 

46. Evaluate x 2 4x 3 y 4 4y 2 if x = 2 and y = -1. 

47. Evaluate a 4 (Z? 2 ) 3 + 2aZ? if a = -2 and fe = 1. 

48. Evaluate 5x 2 - 2y 3 + 3z if jc = 3, y = 2, and z = 4. 

/ 2 \-2 

49. Evaluate (^ J if a = 5 and Z? = 3. 
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50. Evaluate 3 • 5 5 - 10 • 5 + 1. 

51. Evaluate ^%3^. 

52. Evaluate (§|)~ • |. 
Mixed Review 

53. A quiz has ten questions: 7 true/false and 3 multiple choice. The multiple choice questions each have 
four options. How many ways can the test be answered? 

54. Simplify 3a 4 b 4 ■ a" 3 r 4 . 

55. Simplify (x 4 y 2 -xy ) 5 . 

2 

56. Simplify 1 — t-t. 

^ J -vu z -u L v^ 

57. Solve for n : -6(4« + 3) = n + 32. 

8.4 Scientific Notation 

Sometimes in mathematics numbers are huge. They are so huge that we use what is called scientific 
notation. It is easier to work with such numbers when we shorten their decimal places and multiply them 
by 10 to a specific power. In this lesson, you will learn how to use scientific notation by hand and on a 
calculator. 

Powers of 10: 

100,000 = 10 5 

10,000 = 10 4 

1,000 = 10 3 

100 = 10 2 

10 = 10 1 

Using Scientific Notation for Large Numbers 

Example: If we divide 643,297 by 100,000 we get 6.43297. If we multiply this quotient by 100,000, we get 
back to our original number. But we have just seen that 100,000 is the same as 10 5 , so if we multiply 
6.43297 by 10 5 , we should also get our original answer. In other words 6.43297 X 10 5 = 643,297 Because 
there are five zeros, the decimal moves over five places. 

Solution: Look at the following examples: 

2.08 xlO 4 = 20,800 
2.08 xlO 3 = 2,080 
2.08 x 10 2 = 208 
2.08 xlO 1 = 20.8 
2.08x10° = 2.08 

The power tells how many decimal places to move; positive powers mean the decimal moves to the right. 
A positive 4 means the decimal moves four positions the right. 

Example 1: Write in scientific notation. 

317 www.ckl2.org 



653,937,000 

Solution: 653, 937, 000 = 6.53937000 x 100, 000, 000 = 6.53937 x 10 8 

Oftentimes we do not keep more than a few decimal places when using scientific notation and we round the 
number to the nearest whole number, tenth, or hundredth depending on what the directions say. Rounding 
Example 1 could look like 6.5 X 10 8 . 

Using Scientific Notation for Small Numbers 

We've seen that scientific notation is useful when dealing with large numbers. It is also good to use when 
dealing with extremely small numbers. 

Look at the following examples: 

2.08 xlO" 1 = 0.208 
2.08 x 10 -2 = 0.0208 
2.08 x 10" 3 = 0.00208 
2.08 x 10" 4 = 0.000208 

Example 2: The time taken for a light beam to cross a football pitch is 0.0000004 seconds. Write in 
scientific notation. 

Solution: 0.0000004 = 4 x 0.0000001 = 4 x 100 q 0000 =4x^ = 4x 10" 7 

Evaluating Expressions Using Scientific Notation 

When evaluating expressions with scientific notation, it is easiest to keep the powers of 10 together and 
deal with them separately. 

Example: (3.2 x 10 6 ) • (8.7 x 10 11 ) = 3.2 x 8.7 • 10 6 x 10 11 = 27.84 x 10 17 = 2.784 x 10 1 x 10 17 = 2.784 x 10 18 

Solution: It is best to keep one number before the decimal point. In order to do that, we had to make 
27.84 become 2.784 x 10 1 so we could evaluate the expression more simply. 

Example 3: Evaluate the following expression. 

(a) (1.7xl0 6 )-(2.7xl0- n ) 

(b) (3.2xl0 6 )-(8.7xlO n ) 
Solution: 

(a) (1.7 x 10 6 ) • (2.7 x 10" 11 ) = 1.7 x 2.7 • 10 6 x 10" 11 = 4.59 x 10" 5 

(b) (3.2 x 10 6 ) -f (8.7 x 10 11 ) = f^y£ = |f x ^ = 0.368 x 10 6 " 11 = 3.68 x 10" 1 x 10" 5 = 3.68 x 10" 6 
You must remember to keep the powers of ten together, and have 1 number before the decimal. 

Scientific Notation Using a Calculator 

Scientific and graphing calculators make scientific notation easier. To compute scientific notation, use the 
[EE] button. This is [2nd] [,] on some TI models or [10*], which is [2nd] [log]. 

For example to enter 2.6 x 10 5 enter 2.6 [EE] 5. 
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2. 6e5 



2.6e5 

266000 



When you hit [ENTER] the calculator displays 2.6E5 if it's set in Scientific mode OR it displays 260,000 
if it's set in Normal mode. 

Solving Real- World Problems Using Scientific Notation 




Example: The mass of a single lithium atom is approximately one percent of one millionth of one billionth 
of one billionth of one kilogram. Express this mass in scientific notation. 

Solution: We know that percent means we divide by 100, and so our calculation for the mass (in kg) is 



x 



x 



l 



x 



1(T J x 10" b x 10" y x 10 



-9 



100 ~ 1,000,000 ~ 1,000,000,000 ~ 1,000,000,000 

Next, we use the product of powers rule we learned earlier in the chapter. 



10" 2 x 10" 6 x 10" 9 x 10" 9 = i ((-2)+(- 6 )+(- 9 )+(- 9 )) = 10" 26 kg. 
The mass of one lithium atom is approximately 1 x 10 -26 kg. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Scientific Notation (14:26) 

Write the numerical value of the following expressions. 



1. 3.102 xlO 2 

2. 7.4 xlO 4 

3. 1.75 xlO -3 

4. 2.9 xlO" 5 

5. 9.99 xlO" 9 

6. (3.2 xlO 6 ) • 



U xlO 11 ] 



319 



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Figure 8.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/785 



7. (5.2 x 10" 4 ) • (3.8 x 10" 19 ) 

8. (1.7xl0 6 )-(2.7xl0- n ) 

9. (3.2xl0 6 )^(8.7xlO n ) 
10. (5.2 x 1CT 4 ) H- (3.8 x 10~ 19 ) 

1.7xl0 6 )^(2.7xl0- n ) 



11. 



Write the following numbers in scientific notation. 

12. 120,000 

13. 1,765,244 

14. 63 

15. 9,654 

16. 653,937,000 

17. 1,000,000,006 

18. 12 

19. 0.00281 

20. 0.000000027 

21. 0.003 

22. 0.000056 

23. 0.00005007 

24. 0.00000000000954 

25. The moon is approximately a sphere with radius r = 1.08 x 10 3 miles. Use the formula Surface 
Area = 4nr 2 to determine the surface area of the moon, in square miles. Express your answer in 
scientific notation, rounded to two significant figures. 

26. The charge on one electron is approximately 1.60 x 10~ 19 coulombs. One Faraday is equal to the 
total charge on 6.02 X 10 23 electrons. What, in coulombs, is the charge on one Faraday? 

27. Proxima Centauri, the next closest star to our Sun, is approximately 2.5 x 10 13 miles away. If light 
from Proxima Centauri takes 3.7 x 10 4 hours to reach us from there, calculate the speed of light in 
miles per hour. Express your answer in scientific notation, rounded to two significant figures. 

Mixed Review 



28. 14 milliliters of a 40% sugar solution was mixed with 4 milliliters of pure water. What is the 
concentration of the mixture? 
\6x + 3y + 18 

(-15 = lly-5x 
30. Graph the function by creating a table: f(x) — 2x 2 . Use the following values for x : -5 < x < 5. 

2„-6 



29. Solve the system 



31. Simplify ^g 
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Your answer should have only positive exponents. 

320 



32. Each year Americans produce about 230 million tons of trash (Source: http://www.learner.org/ 
interactives/garbage/solidwaste.html). There are 307,006,550 people in the United States. 
How much trash is produced per person per year? 

33. The volume of a 3-dimesional box is given by the formula: V = l(w)(h), where / = length, w = width, 
and h = height of the box. The box holds 312 cubic inches and has a length of 12 inches and a width 
of 8 inches. How tall is the box? 

Quick Quiz 

1. Simplify: <^/'>" 

2. The formula A = 1, 500 (1. 0025) f gives the total amount of money in a bank account with a balance of 
$1,500.00, earning 0.25% interest, compounded annually. How much money would be in the account 
five years in the past? 

3. True or false? (|)" 3 = -^ 

8.5 Exponential Growth Functions 

In previous lessons, we have seen the variable as the base. In exponential functions, the exponent is the 
variable and the base is a constant. 

General Form of an Exponential Function: y = a(b) x , where a = initial value and 

b = growth factor 

In exponential growth situations, the growth factor must be greater than one. 

b> 1 

Example: A colony of bacteria has a population of 3,000 at noon on Sunday. During the next week, the 
colony's population doubles every day. What is the population of the bacteria colony at noon on Saturday? 




Solution: Make a table of values and calculate the population each day. 

Table 8.1: 



Day (Sun) 


1 (Mon) 


2 (Tues) 


3 (Wed) 


4 

(Thurs) 


5 (Fri) 


6 (Sat) 


Population 3 
(thou- 
sands) 


6 


12 


24 


48 


96 


192 



321 www.ckl2.org 



To get the population of bacteria for the next day we multiply the current day's population by 2 because 
it doubles every day. If we define x as the number of days since Sunday at noon, then we can write the 
following: P = 3 • 2 X . This is a formula that we can use to calculate the population on any day. For 
instance, the population on Saturday at noon will be P = 3 • 2 6 = 3 • 64 = 192 thousand bacteria. We use 
x = 6, since Saturday at noon is six days after Sunday at noon. 

Graphing Exponential Functions 

Example: Graph the equation using a table of values y = 2 X . 

Solution: Make a table of values that includes both negative and positive values of x. Substitute these 
values for x to get the value for the y variable. 

Table 8.2: 




1 
2 
3 



4 
1 

2 
1 

2 

4 



Plot the points on the coordinate axes to get the graph below. Exponential functions always have this 
basic shape: They start very small and then once they start growing, they grow faster and faster, and soon 
they become huge. 







8 












A 












4 























£.- 






3 - 


2 - 


1 


1 2 3 



Comparing Graphs of Exponential Functions 

The shape of the exponential graph changes if the constants change. The curve can become steeper or 
shallower. 

Earlier in the lesson, we produced a graph for y = 2 X . Let's compare that graph with the graph of y = 3-2*. 



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322 



Table 8.3: 




1 
2 
3 



1 

2 1 



2- 2 = 3 
2" 1 = 3 
2° = 3 

2 1 = 6 

2 2 = 3-4 = 12 

2 3 = 3 • 8 = 24 



We can see that the function y — 3 • 2 X is bigger than the function j — 2 X . In both functions, the value of 
y doubles every time x increases by one. However, y = 3 • 2 X starts with a value of 3, while y = 2 X starts 
with a value of 1, so it makes sense that y = 3 • 2 X would be bigger. 









25 
on 


y=3.2 x / 


1 








1 R 
















TO 
















m 
















IU 
















c 








y = 








O 










1 -3 -2 -1 


12 3 4 


-5 


I I I I 



= r 



Solving Real- World Problems with Exponential Growth 

Example: The population of a town is estimated to increase by 15% per year. The population today is 
20,000. Make a graph of the population function and find out what the population will be ten years from 
now. 




Solution: The population is growing at a rate of 15% each year. When something grows at a percent, this 
is a clue to use exponential functions. 

Remember, the general form of an exponential function is y = a(b) x , where a is the beginning value and b 
is the total growth rate. The beginning value is 20,000. Therefore, a = 20,000. 

The population is keeping the original number of people and adding 15% more each year. 



323 



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100% + 15% = 115% = 1.15 

Therefore, the population is growing at a rate of 115% each year. Thus, b = 1.15. 
The function to represent this situation is y = 20,000 (1.15)*. 
Now make a table of values and graph the function. 

Table 8.4: 



y = 20-(1.15) x 



-10 

-5 



5 

10 



4.9 

9.9 

20 

40.2 

80.9 




-10-8 



Notice that we used negative values of x in our table. Does it make sense to think of negative time? In 
this case x = -5 represents what the population was five years ago, so it can be useful information. 

The question asked in the problem was "What will be the population of the town ten years from now?" To 
find the population exactly, we use x = 10 in the formula. We find y = 20,000 • (1.15) 10 = 80,912. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Exponential Growth Functions (7:41) 



1. What is the general equation for an exponential equation? What do the variables represent? 

2. How is an exponential growth equation different from a linear equation? 

3. What is true about the growth factor of an exponential equation? 



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324 




Figure 8.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/787 

4. True or false? An exponential growth function has the following form: f(x) = a(b) x , where a > 1 
and b < 1? 

5. What is the y-intercept of all exponential growth functions? 

Graph the following exponential functions by making a table of values. 

6. y = 3 X 

7. y = 2 X 

8. y = 5 • 3* 

9. y = \ • 4 X 

10. f{x) = ± ■ 7* 

11. f{x) = 2-3* 

12. y = 40 • 4* 

13. y = 3 • 10 x 

Solve the following problems. 

14. The population of a town in 2007 is 113,505 and is increasing at a rate of 1.2% per year. What will 
the population be in 2012? 

15. A set of bacteria begins with 20 and doubles every 2 hours. How many bacteria would be present 15 
hours after the experiment began? 

16. The cost of manufactured goods is rising at the rate of inflation, about 2.3%. Suppose an item costs 
$12 today. How much will it cost five years from now due to inflation? 

17. A chain letter is sent out to 10 people telling everyone to make 10 copies of the letter and send each 
one to a new person. Assume that everyone who receives the letter sends it to 10 new people and 
that it takes a week for each cycle. How many people receive the letter in the sixth week? 

18. Nadia received $200 for her 10^ birthday. If she saves it in a bank with a 7.5% interest rate com- 
pounded yearly, how much money will she have in the bank by her 21^ birthday? 

Mixed Review 



19. Suppose a letter is randomly chosen from the alphabet. What is the probability the letter chosen is 
M, K, or L? 

20. Evaluate t 4 • t\ when t = 9. 

21. Simplify 28- (x- 16). 

22. Graph y - 1 = |(jc + 6). 



325 



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8.6 Exponential Decay Functions 

In the last lesson, we learned how to solve expressions that modeled exponential growth. In this lesson, we 
will be learning about exponential decay functions. 

General Form of an Exponential Function: y = a(b) x , where a = initial value and 

b = growth factor 

In exponential decay situations, the growth factor must be a fraction between zero and one. 

0<b< 1 

Example: For her fifth birthday, Nadia's grandmother gave her a full bag of candy. Nadia counted her 
candy and found out that there were 160 pieces in the bag. Nadia loves candy, so she ate half the bag on 
the first day. Her mother told her that if she continues to eat at that rate, it will be gone the next day and 
she will not have any more until her next birthday. Nadia devised a clever plan. She will always eat half 
of the candy that is left in the bag each day. She thinks that she will get candy every day and her candy 
will never run out. How much candy does Nadia have at the end of the week? Would the candy really last 
forever? 




Solution: Make a table of values for this problem. 

Table 8.5: 



Day 


1 


2 


3 


4 


5 


6 


7 


# of 160 
Candies 


80 


40 


20 


10 


5 


2.5 


1.25 



You can see that if Nadia eats half the candies each day, then by the end of the week she has only 1.25 
candies left in her bag. 

Write an equation for this exponential function. Nadia began with 160 pieces of candy. In order to get 
the amount of candy left at the end of each day, we keep multiplying by \. Because it is an exponential 
function, the equation is: 

l x 

y = i60.- 
Graphing Exponential Decay Functions 

Example: Graph the exponential function y = 5 • \h) . 
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Solution: Start by making a table of values. Remember when you have a number to the negative power, 
you are simply taking the reciprocal of that number and taking it to the positive power. Example: ( \ ) = 

(f) 2 - 22 - 

Table 8.6: 



-«■(»" 




1 

2 



y = 5(^ = 40 

y = 5(^ = 10 

v = 5(±)° = 5 

y=m 2 =i 



Now graph the function. 




1 2 3 x 



Using the Property of Negative Exponents, the equation can also be written as 5 • 2 x . 

Comparing Graphs of Exponential Decay Functions 

Exponential growth and decay graphs look like opposites and can sometimes be mirror images. 

Example: Graph the functions y — A x and 4~ x on the same coordinate axes. 

Solution: Here is the table of values and the graph of the two functions. 

Looking at the values in the table, we see that the two functions are "reverse images" of each other in the 
sense that the values for the two functions are reciprocals. 

Table 8.7: 



y = 4 x 



y = 4T* 



y 
y 



4-3 
4-2 



64 
J_ 

16 



y 
y 



4 -(-3) 
4-(-2) 



64 
16 



327 



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Table 8.7: (continued) 



y = 4 x 



y 



4-x 




1 
2 
3 



y = 4° = 1 
y = 4 1 = 4 
j = 4 2 = 16 
j = 4 3 = 64 



j = 4-H) = 4 
j = 4"(°) = 1 
y = 4-« 



4"(2) 
4-(3) 



1 

4 

J_ 

16 

J_ 

64 



Here is the graph of the two functions. Notice that these two functions are mirror images if the mirror is 
placed vertically on the v-axis. 




Solving Real- World Problems Involving Exponential Decay Func- 
tions 

Example: The cost of a new car is $32,000. It depreciates at a rate of 15% per year. This means that it 
loses 15% of its value each year. 

• Draw the graph of the car's value against time in years. 

• Find the formula that gives the value of the car in terms of time. 

• Find the value of the car when it is four years old. 

Solution: Start by making a table of values. To fill in the values we start with 32,000 when t — 0. Then we 
multiply the value of the car by 85% for each passing year. (Since the car loses 15% of its value, it keeps 
85% of its value). Remember 85% = 0.85. 

Table 8.8: 



Time 



Value (Thousands) 




1 
2 
3 
4 
5 



32 

27.2 
23.1 
19.7 
16.7 
14.2 



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328 




6 8 10 
time (in years) 

The general formula is y = a(b) x . 

In this case: y is the value of the car, x is the time in years, a = 32, 000 is the starting amount in thousands, 
and b = 0.85 since we multiply the value in any year by this factor to get the value of the car in the following 
year. The formula for this problem is y = 32, 000(0. 85)*. 

Finally, to find the value of the car when it is four years old, we use x = 4 in the formula. Remember the 
value is in thousands. 



y = 32,000(0.85) 4 = 16,704. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Exponential Decay Functions (10:51) 




Figure 8.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/788 



1. Define exponential decay. 

2. What is true about "b" in an exponential decay function? 

3. Suppose f(x) = a(b) x . What is /(0)? What does this mean in terms of the y-intercept of an 
exponential function? 

Graph the following exponential decay functions. 



329 



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4. 


y = 


IX 

■ 5 


/ o 


\JC 


5. 


y = 


4- 


(1 


) 


6. 


y = 


3" 


X 




7. 


y = 


3 

4 ' 


•6" 


-x 



Solve the following application problems. 

8. The cost of a new ATV (all-terrain vehicle) is $7200. It depreciates at 18% per year. 

(a) Draw the graph of the vehicle's value against time in years. 

(b) Find the formula that gives the value of the ATV in terms of time. 

(c) Find the value of the ATV when it is ten years old. 

9. Michigan's population is declining at a rate of 0.5% per year. In 2004, the state had a population of 
10,112,620. 

(a) Write a function to express this situation. 

(b) If this rate continues, what will the population be in 2012? 

(c) When will the population of Michigan reach 9,900,000? 

(d) What was the population in the year 2000, according to this model? 

10. A certain radioactive substance has a half-life of 27 years. An organism contains 35 grams of this 
substance on day zero. 

(a) Draw the graph of the amount remaining. Use these values for x : x = 0, 27, 54, 81, 108, 135. 

(b) Find the function that describes the amount of this substance remaining after x days. 

(c) Find the amount of radioactive substance after 92 days. 

11. The percentage of light visible at d meters is given by the function V(d) = 0.70^. 

(a) What is the growth factor? 

(b) What is the initial value? 

(c) Find the percentage of light visible at 65 meters. 

12. A person is infected by a certain bacterial infection. When he goes to the doctor, the population of 
bacteria is 2 million. The doctor prescribes an antibiotic that reduces the bacteria population to \ 
of its size each day. 

(a) Draw the graph of the size of the bacteria population against time in days. 

(b) Find the formula that gives the size of the bacteria population in terms of time. 

(c) Find the size of the bacteria population ten days after the drug was first taken. 

(d) Find the size of the bacteria population after two weeks (14 days). 

Mixed Review 

13. The population of Kindly, USA is increasing at a rate of 2.14% each year. The population in the 
year 2010 is 14,578. 

(a) Write an equation to model this situation. 

(b) What would the population of Kindly be in the year 2015? 

(c) When will the population be 45,000? 

14. The volume of a sphere is given by the formula v = 3 at 3 . Find the volume of a sphere with a diameter 
of 11 inches. 

15. Simplify^- J .x°y. 

16. Simplify 3(x 2 y 3 ^) 2 - 

17. Rewrite in standard form: y - 16 + x = -Ax + fry + 1. 

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8.7 Geometric Sequences and Exponential Func- 
tions 



Which would you prefer: being given one million dollars, or one penny the first day, double that penny the 
next day, and then double the previous day's pennies and so on for a month? 

At first glance you would think that a million dollars would be more. However, let's use geometric sequences 
before we decide to see how the pennies add up. You start with a penny the first day and keep doubling 
each day until the end of the month (30 days). 



I st Day 
2 nd Day 
3 rd Day 
4 th Day 
30'* Day 



1 penny = 2 
2 pennies = 2 1 
4 pennies = 2 
8 pennies = 2 
= 2 29 




2 2 9 = 536,870,912 pennies or $5,368,709, which is well over five times greater than $1,000,000.00. 

Geometric Sequence: a sequence of numbers in which each number in the sequence is found by multi- 
plying the previous number by a fixed amount called the common ratio. 



jh 



term in a geometric sequence a n = air n {a\ = first term, r = common ratio) 



The Common Ratio of a Geometric Sequence 

The common ratio, r, in any geometric sequence can be found by dividing any term by the preceding term. 
If we know the common ratio in a sequence then we can find any term in the sequence. 

Example 1: Find the eighth term in the geometric sequence. 

1,2,4,... 



Solution First we need to find the common ratio r 



2. 



The eighth term is given by the formula 2 = 1 • 2 7 = 128. 

In other words, to get the eighth term we started with the first term, which is 1, and multiplied by two 
seven times. 



Graphing Geometric Sequences 

Exponential graphs and geometric sequence graphs look very much alike. Exponential graphs are contin- 
uous, however, and the sequence graphs are discrete with distinct points {1 st term and 2 nd term, etc). 



331 



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Example: A population of bacteria in a Petri dish increases by a factor of three every 24 hours. The 
starting population is 1 million bacteria. This means that on the first day the population increases to 3 
million on the second day to 9 million and so on. 

Solution: The population of bacteria is continuous. Even though we measured the population only every 
24 hours, we know that it does not get from 1 million to 3 million all at once. Rather, the population 
changes bit by bit over the 24 hours. In other words, the bacteria are always there, and you can, if you so 
wish, find out what the population is at any time during a 24-hour period. 

When we graph an exponential function, we draw the graph with a solid curve to show the function has 
values at any time during the day. On the other hand, when we graph a geometric sequence, we draw 
discrete points to show the sequence has value only at those points but not in between. 

Here are graphs for the two examples previously given: 



Exponential Function 




12 3 4 

time (in days) 



3 
S3 

! 

O 

3* 



4ee- 



Geometric Sequence 



60- 



m- 



Ad- 
26- 



1 L 



t 



3 4 

Stack number 



Solving Real- World Problems Involving Geometric Sequences 

Example: A courtier presented the Indian king with a beautiful, hand-made chessboard. The king asked 
what he would like in return for his gift and the courtier surprised the king by asking for one grain of rice 
on the first square, two grains on the second, four grains on the third, etc. The king readily agreed and 
asked for the rice to be brought (from Meadows et al. 1972, p. 29 via Porritt 2005). How many grains of 
rice does the king have to put on the last square? 

Solution: A chessboard is an 8 x 8 square grid, so it contains a total of 64 squares. 

The courtier asked for one grain of rice on the first square, 2 grains of rice on the second square, 4 grains 
of rice on the third square and so on. We can write this as a geometric sequence. 

1,2,4,... 

The numbers double each time, so the common ratio is r = 2. 

The problem asks how many grains of rice the king needs to put on the last square. What we need to find 
is the 64^ term in the sequence. This means multiplying the starting term, 1, by the common ratio 64 
times in a row. Let's use the formula. 

a n = a\r n ~ l , where a n is the n th term, a\ Is the first term and r is the common ratio. 

a 6A = 1 • 2 63 = 9, 223, 372, 036, 854, 775, 808 grains of rice. 



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332 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Geometric Sequences (10:45) 




Figure 8.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/789 



1. Define a geometric sequence. 

2. Using the chessboard example, how many grains of rice should be placed on the: 

(a) Fourth square? 

(b) Tenth square? 

(c) Twenty-fifth square? 

(d) 60 th square? 

3. Is the following an example of a geometric sequence? Explain your answer. -1, 1, -1, 1, -1, 

4. Use the Petri dish example from the lesson. At what time are 25,000 bacteria in the dish? 

Determine the constant ratio, r, for each geometric sequence. 

5. 8, 6,... 

6. 2, 4, 8, 16,... 
7 q q I I 

8. 2, -8, 32, -128 

Determine the first five terms of each geometric sequence. 

9. a x = 2,r = 3 

10. ai =90,r = -i 

11. ai = 6,r = -2 

Find the missing terms in each geometric series: 



12. 3, _ 

13. 81, 
14 2 



_, 48, 192, 



2 
-' 3' 



Find the indicated term of each geometric series. 



333 



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15. a\ = 4, r = 2 Find a$. 

16. a\ = -7, r = -| Find (34. 

17. ^i = -10, r = -3 Find a\§. 



18. A ball is tossed from a height of four feet. Each bounce is 80% as high as the previous bounce. 

(a) Write an equation to represent the situation. 

(b) How high is the ball after the fifth bounce? 

19. An ant walks past several stacks of Lego blocks. There is one block in the first stack, three blocks in 
the second stack, and nine blocks in the third stack. In fact, in each successive stack there are triple 
the number of blocks there were in the previous stack. 

(a) How many blocks are in the eighth stack? 

(b) When is the stack 343 blocks high? 

20. A super-ball has a 75% rebound ratio. When you drop it from a height of 20 feet, it bounces and 
bounces and bounces... 

(a) How high does the ball bounce after it strikes the ground for the third time? 

(b) How high does the ball bounce after it strikes the ground for the seventeenth time? 

21. Anne goes bungee jumping off a bridge above water. On the initial jump, the bungee cord stretches 
by 120 feet. On the next bounce, the stretch is 60% of the original jump and each additional bounce 
stretches the rope by 60% of the previous stretch. 

(a) What will the rope stretch be on the third bounce? 

(b) What will the rope stretch be on the 12^ bounce? 

22. A virus population doubles every 30 minutes. It begins with a population of 30. 

(a) How many viral cells will be present after 5 hours? 

(b) When will it reach 1,000,000 cells? Round to the nearest half-hour. 

23. The half-life of the prescription medication Amiodarone is 25 days. Suppose a patient has a single 
dose of 12 mg of this drug in her system. 

(a) How much Amiodarone will be in the patient's system after four half-life periods? 

(b) When will she have less than 3 mg of the drug in her system? 

(c) What is the growth factor of this situation? 

Mixed Review 

24. Translate into an algebraic sentence: A number squared is less than 15 more than twice that number. 

25. Give the slope and y-intercept of y = |x - 7. 

26. Evaluate 10! 

27. Convert 6 miles to yards. 

28. Simplify b -^. 

29. Simplify 3x 2 ■ x 6 + 4x 3 r\ 

_ 1 

30. Evaluate (§|) 3 . 

8.8 Problem- Solving Strategies 

We have to deal with problem solving in everyday life. Therefore, it is important to know the steps you 
must take when problem solving. 

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Example: Suppose $4000 is invested at a 6% interest rate compounded annually. How much money will 
there be in the bank at the end of five years? At the end of 20 years? 

Solution: Read the problem and summarize the information. 

$4000 is invested at a 6% interest rate compounded annually. We want to know how much money we have 
after five years. 

• Assign variables. Let x = time in years and y = amount of money in investment account. 

• We start with $4000 and each year we apply a 6% interest rate on the amount in the bank. 

• The pattern is that each year we multiply the previous amount by the factor of 100% + 6% = 106% = 
1.06. 

• Complete a table of values. 

Table 8.9: 



Time 

(years) 





1 


2 


3 


4 


5 


Investment 
Amount 

($) 


4000 


4240 


4494.40 


4764.06 


5049.91 


5352.90 



Using the table, we see that at the end of five years we have $5352.90 in the investment account. 

In the case of five years, we don't need an equation to solve the problem. However, if we want the amount 
at the end of 20 years, it becomes too difficult to constantly multiply. We can use a formula instead. 

Since we take the original investment and keep multiplying by the same factor of 1.06, that means we can 
use exponential notation. 

y = 4000 • (1.06) x 
To find the amount after five years we use x = 5 in the equation. 

y = 4000 • (1.06) 5 = $5352.90 

To find the amount after 20 years we use x = 20 in the equation. 

y = 4000 • (1.06) 20 = $12, 828.54 

To check our answers we can plug in some low values of x to see if they match the values in the table: 

x = 4000 • (1.06)0 = 4000 

x= 1 4000 -(1.06)1 = 4240 

x = 2 4000 • (1.06)2 = 4494.40 

The answers make sense because after the first year, the amount goes up by $240 (6% of $4000). The 
amount of increase gets larger each year and that makes sense because the interest is 6% of an amount 
that is larger and larger every year. 

Multimedia Link: To learn more about how to use the correct exponential function, visit the http: 
//regent sprep.org/REgents/math/ALGEBRA/AE7/ExpDecayL. htm - algebra lesson page by RegentsPrep. 

335 www.ckl2.org 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Word Problem Solving (7:21) 




Figure 8.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/554 

Apply the problem-solving techniques described in this section to solve the following problems. 

1. Half-life Suppose a radioactive substance decays at a rate of 3.5% per hour. What percent of the 
substance is left after six hours? 

2. Population decrease In 1990, a rural area has 1200 bird species. If species of birds are becoming 
extinct at the rate of 1.5% per decade (10 years), how many bird species will there be left in year 
2020? 

3. Growth Nadia owns a chain of fast food restaurants that operated 200 stores in 1999. If the rate of 
increase is 8% annually, how many stores does the restaurant operate in 2007? 

4. Investment Peter invests $360 in an account that pays 7.25% compounded annually. What is the 
total amount in the account after 12 years? 



8.9 Chapter 8 Review 

Define the following words. 

1. Exponent 

2. Geometric Sequence 

Use the product properties to simplify the following expressions. 

3. 5 -5 -5 -5 

4. (3xV) • (4xy 2 ) 

5. a 3 ■ a 5 ■ a 6 

6. (y 3 ) 5 

7. (x-x 3 -x 5 ) 10 

8. (2a 3 b 3 ) 2 ' 



Use the quotient properties to simplify the following expressions. 
www.ckl2.org 336 



9. 
10. 
11. 

12. 



a 

a 5 b 4 
a 3 b 2 



Simplify the following expressions. 



6i 

6 5 

z! 

r 5 
Zi 

7 6 
J2_ 
/3 



13. 

14. 

15. 

16. , 

x° 

17. \^ 
\2 



18. (a?) 



Write the following in scientific notation. 

20. 557,000 

21. 600,000 

22. 20 

23. 0.04 

24. 0.0417 

25. 0.0000301 

26. The distance from the Earth to the moon: 384,403 km 

27. The distance from Earth to Jupiter: 483,780,000 miles 

28. According to the CDC, the appropriate level of lead in drinking water should not exceed 15 parts 
per billion (EPA's Lead & Copper Rule). 

Write the following in standard notation. 

29. 3.53 xlO 3 

30. 89 XlO 5 

31. 2.12 xlO 6 

32. 5.4 xlO 1 

33. 7.9 xlO" 3 

34. 4.69 xlO" 2 

35. 1.8 xlO" 5 

36. 8.41 xlO" 3 

Make a graph of the following exponential growth/decay functions. 

37. y = 3- (6) x 

38. 7 = 2- (ff 

39. Marissa was given 120 pieces of candy for Christmas. She ate one- fourth of them each day. Make a 
graph to find out in how many days Marissa will run out of candy. 

337 www.ckl2.org 



40. Jacoby is given $1500 for his graduation. He wants to invest it. The bank gives a 12% investment 
rate each year. Make a graph to find out how much money Jacoby will have in the bank after six 
years. 

Determine what the common ratio is for the following geometric sequences to finish to sequence. 

41. 1, 3, , , 81 

42. , 5, , 125, 625 

43. 7, , 343, 2401, 

44. 5, 1.5, , 0.135, 

45. The population of ants in Ben's room increases three times daily. He starts with only two ants. Make 
a geometric graph to determine how many ants will be in Ben's room at the end of a 30-day month 
if he does not take care of the problem. 

8.10 Chapter 8 Test 

Simplify the following expressions. 

1. x 3 -x 4 -x 5 

2. (a 3 ) 7 

3. (yhy 

4. a 4 



5. 

6. 

7. 



x 3 y 2 



/3£V 
\ 9x 6 y 5 

31 

3 4 



9. W 

Complete the following story problems. 

10. The intensity of a guitar amp is 0.00002. Write this in scientific notation. 

11. Cole loves turkey hunting. He already has two after his first day of the hunting season. If this number 
doubles each day, how many turkeys will Cole have after 11 days? Make a table for the geometric 
sequence. 

12. The population of a town increases by 20% each year. It first started with 89 people. What will the 
population be of the town after 15 years? 

13. A radioactive substance decays 2.5% every hour. What percent of the substance will be left after 
nine hours? 

14. After an exterminator comes to a house to exterminate cockroaches, the bugs leave the house at a 
rate of 16% an hour. How long will it take 55 cockroaches to leave a house after the exterminator 
comes there? 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/flexr/chapter/9618. 

www.ckl2.org 338 



Chapter 9 

Polynomials and Factoring; 
More on Probability 



This chapter will present a new type of function: the polynomial. Chances are, polynomials will be new 
to you. However, polynomials are used in many careers and real life situations - to model the population 
of a city over a century, to predict the price of gasoline, and to predict the volume of a solid. This chapter 
will also present basic factoring - breaking a polynomial into its linear factors. This will help you solve 
many quadratic equations found in Chapter 10. 



9.1 Addition and Subtraction of Polynomials 

So far we have discussed linear functions and exponential functions. This lesson introduces polynomial 
functions. 

Definition: A polynomial is an expression made with constants, variables, and positive integer exponents 
of the variables. 

An example of a polynomial is: 4x 3 + 2x 2 - 3x + 1. There are four terms: 4x 3 , 2x 2 , 3x, and 1. The numbers 
appearing in each term in front of the variable are called the coefficients. 4, 2, and 3 are coefficients 
because those numbers are in front of a variable. The number appearing all by itself without a variable is 
called a constant. 1 is the constant because it is by itself. 

Example 1: Identify the following expressions as polynomials or non-polynomials. 

(a) 5x 2 - 2x 

(b) 3x 2 - 2x~ 2 

(c) xyfx-1 



339 www.ckl2.org 



(d) A 

(e) 4jc^ 

(f) 4xy 2 - 2x 2 y - 3 + y 3 - 3x 3 
Solution: 

(a) 5x 2 - 2x This is a polynomial. 

(b) 3x 2 - 2x~ 2 This is not a polynomial because it has a negative exponent. 

(c) xyfx-1 This is not a polynomial because is has a square root. 

(d) -^q-j- This is not a polynomial because the power of x appears in the denominator. 

(e) 4x3 This is not a polynomial because it has a fractional exponent. 

(f) 4xy 2 - 2x y - 3 + y 3 - 3x 3 This is a polynomial. 

Classifying Polynomials by Degree 

The degree of a polynomial is the largest exponent of a single term. 

• 4x 3 has a degree of 3 and is called a cubic term or 3 rd order term. 

• 2x 2 has a degree of 2 and is called a quadratic term or 2 nd order term. 

• -3x has a degree of 1 and is called a linear term or 1 st order term. 

• 1 has a degree of because there is no variable. 

Polynomials can have more than one variable. Here is another example of a polynomial: t 4 - 6s 3 t 2 - 12st-\- 
4s 4 - 5. This is a polynomial because all exponents on the variables are positive integers. This polynomial 
has five terms. Note: The degree of a term is the sum of the powers on each variable in the term. 

t 4 has a degree of 4, so it's a 4 th order term. 

-6s 3 t 2 has a degree of 5, so it's a 5 th order term. 

-12^ has a degree of 2, so it's a 2 nd order term. 

4s 4 has a degree of 4, so it's a 4 th order term. 

-5 is a constant, so its degree is 0. 

Since the highest degree of a term in this polynomial is 5, this is a polynomial of degree 5 or a 5 th order 
polynomial. 

Example 2: Identify the coefficient on each term, the degree of each term, and the degree of the polynomial. 

x 4 - 3x 3 y 2 + 8x - 12 

Solution: The coefficients of each term in order are 1, -3, 8 and the constant is -12. 

The degrees of each term are 4, 5, 1, and 0. Therefore, the degree of the polynomial is 5. 

A monomial is a one-termed polynomial. It can be a constant, a variable, or a combination of constants 
and variables. Examples of monomials are: b 2 \ 6; -2ab 2 ; \x 2 

Rewriting Polynomials in Standard Form 

Often, we arrange the terms in a polynomial in standard from in which the term with the highest degree 
is first and is followed by the other terms in order of decreasing power. The first term of a polynomial in 

www.ckl2.org 340 



this form is called the leading term, and the coefficient in this term is called the leading coefficient. 

Example 3: Rearrange the terms in the following polynomials so that they are in standard form. Indicate 
the leading term and leading coefficient of each polynomial. 

(a) 7 - 3x 3 + 4* 

(b) ab - a 3 + 2b 
Solution: 

(a) 7 - 3x 3 + 4x is rearranged as -3x 3 + 4x + 7. The leading term is -3x 3 and the leading coefficient is -3. 

(b) ab - a 3 + 2b is rearranged as -a 3 + ab + 2b. The leading term is -a 3 and the leading coefficient is -1. 

Simplifying Polynomials 

A polynomial is simplified if it has no terms that are alike. Like terms are terms in the polynomial that 
have the same variable(s) with the same exponents, but they can have different coefficients. 

2x 2 y and 5x 2 y are like terms. 

6x 2 y and 6xy 2 are not like terms. 

If we have a polynomial that has like terms, we simplify by combining them. 

x + 6xy - 4xy + y 

/ \ 

Like terms 

This polynomial is simplified by combining the like terms 6xy - 4xy = 2xy. We write the simplified 
polynomial as x 2 + 2xy + y 2 . 

Example 4: Simplify by collecting and combining like terms. 

a 3 b 3 - 5ab 4 + 2a 3 b - a 3 b 3 + 3ab 4 - a 2 b 

Solution: Use the Commutative Property of Addition to reorganize like terms then simplify. 

= {a 3 b 3 - a 3 b 3 ) + {-bab A + 3ab 4 ) + 2a 3 b - a 2 b 
= - 2ab 4 + 2a 3 b - a 2 b 
= -2ab A + 2a 3 b - a 2 b 

Adding and Subtracting Polynomials 

To add or subtract polynomials, you have to group the like terms together and combine them to simplify. 
Example 5: Add and simplify 3x 2 - 4x + 7 and 2x 3 - 4x 2 - Qx + 5. 
Solution: Add 3x 2 - 4x + 7 and 2x 3 - 4x 2 - 6x + 5. 

(3x 2 - 4jc + 7) + {2x 3 - 4x 2 - 6x + 5) = 2x 3 + {3x 2 - 4x 2 ) + (-4* - 6x) + (7 + 5) 

= 2x 3 -jc 2 -10x+12 

Multimedia Link: For more explanation of polynomials, visit http://www.purplemath.com/modules/ 
polydefs.htm - Purplemath's website. 

341 www.ckl2.org 



Example 6: Subtract 5b 2 - 2a 2 from 4a 2 - Sab - 9b 2 . 
Solution: 

(4a 2 - 8ab - 9b 2 ) - (5b 2 - 2a 2 ) = [(4a 2 - (-2a 2 )} + (-9b 2 - 5b 2 ) - 8ab 

= 6a 2 - Ub 2 - Sab 

Solving Real- World Problems Using Addition or Subtraction of 
Polynomials 

Polynomials are useful for finding the areas of geometric objects. In the following examples, you will see 
this usefulness in action. 

Example 7: Write a polynomial that represents the area of each figure shown. 

(a) x y 




Solution: The blue square has area: y • y = y 2 . 

The yellow square has area: x • x = x 2 . 

The pink rectangles each have area: x • y = xy. 

Test area = y 2 + x 2 + xy + xy 
= y 2 + x 2 + 2xy 

To find the area of the green region we find the area of the big square and subtract the area of the little 
square. 

The big square has area y • y = y 2 . 

The little square has area x • x = x 2 . 

Area of the green region = y 2 - x 2 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 



www.ckl2.org 



342 



number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Addition and Subtraction of Polynomials (15:59) 




Figure 9.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/790 



Define the following key terms. 

1. Polynomial 

2. Monomial 

3. Degree 

4. Leading coefficient 

For each of the following expressions, decide whether it is a polynomial. Explain your answer. 

5. x 2 + 3x^ 

6. \x 2 y-9y 2 

7. 3x~ 3 

o 2,2 1 

Express each polynomial in standard form. Give the degree of each polynomial. 

9. 3-2jc 

10. 8jc 4 -x + 5x 2 + 11jc 4 -10 

11. 8-4jc + 3x 3 

12. -16 + 5/ 8 -7/ 3 

13. -5 + 2x - 5x 2 + 8x 3 

14. x 2 - 9x 4 + 12 

Add and simplify. 

15. (jc + 8) + (-3x - 5) 

16. (8r 4 - 6r 2 - 3r + 9) + (3r 3 + 5r 2 + Ylr - 9) 

17. \-2x 2 + 4x - 12) + (7x + x 2 ) 

18. (2a 2 b - 2a + 9) + (5a 2 b - 4/? + 5) 

19. (6.9a 2 - 2.3b 2 + 2ab) + (3.1a - 2.5b 2 + b) 

Subtract and simplify. 

20. (-/+15r 2 )-(5r 2 + 2;-9) 



343 



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21. (-y 2 + 4y - 5) - (5y 2 + 2j + 7) 

22. (-/i 7 + 2/r 5 + 13/r 3 + 4h 2 -h-l)- (-3h 5 + 20/j 3 - 3/i 2 + 8h-4) 

23. (-5m 2 - m) - (3m 2 + 4m - 5) 

24. (2a 2 Z> - 3afc 2 + ha 2 b 2 ) - (2a 2 fc 2 + 4a 2 b - 5b 2 ) 

Find the area of the following figures. 




27. 



X 
X 



2x 



28. 





^b 



Mixed Review 

(y = I X - 4 

29. Solve by graphing < 

(y = — 4jc + 10 

30. Solve for u: 12 = -f . 

31. Graph y = |x - 4| + 3 on a coordinate plane. 

(a) State its domain and range. 

(b) How has this graph been shifted from the parent function f(x) = |jc|? 

32. Two dice are rolled. The sum of the values are recorded. 

(a) Define the sample space. 

(b) What is the probability the sum of the dice is nine? 



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344 



33. Consider the equation y = 6500(0. 8)*. 

(a) Sketch the graph of this function. 

(b) Is this exponential growth or decay? 

(c) What is the initial value? 

(d) What is its domain and range? 

(e) What is the value when x = 9.5? 

34. Write an equation for the line that is perpendicular to y = -5 and contains the ordered pair (6, -5) 

9.2 Multiplication of Polynomials 

When multiplying polynomials together, we must remember the exponent rules we learned in the last 
chapter, such as the Product Rule. This rule says that if we multiply expressions that have the same 
base, we just add the exponents and keep the base unchanged. If the expressions we are multiplying have 
coefficients and more than one variable, we multiply the coefficients just as we would any number. We also 
apply the product rule on each variable separately. 

Example: (2x 2 y 3 ) x (3x 2 y) = (2 • 3) X (r 2 • x 2 ) x (y 3 • y) = 6x 4 y 4 

Multiplying a Polynomial by a Monomial 

This is the simplest of polynomial multiplications. Problems are like that of the one above. 
Example 1: Multiply the following monomials. 
(a) (2x 2 )(5x 3 ) 

(c) (3xy 5 )(-6*V) 

(d) (-12a 2 b 3 c 4 )(-3a 2 b 2 ) 
Solution: 

(a) (2x 2 )(5x 3 ) = (2 • 5) • (x 2 • x 3 ) = 10x 2 + 3 = 10x 5 

(c) (3xy 5 )(-6x 4 y 2 ) = -18x 1+ V +2 = -18jcV 

(d) (-12a 2 b 3 c 4 )(-3a 2 b 2 ) = 36a 2 +V+ 2 c 4 = 36^ 5 c 4 

To multiply monomials, we use the Distributive Property. 

Distributive Property: For any expressions a, b 1 and c, a{b + c) = ab + ac. 

This property can be used for numbers as well as variables. This property is best illustrated by an area 
problem. We can find the area of the big rectangle in two ways. 

a 




One way is to use the formula for the area of a rectangle. 

345 www.ckl2.org 



Area of the big rectangle = Length X Width 
Length = a, Width — b + c 
Area = ax (b + c) 

The area of the big rectangle can also be found by adding the areas of the two smaller rectangles. 

Area of red rectangle = ab 
Area of blue rectangle = ac 
Area of big rectangle = ab + ac 

This means that a{b + c) = ab + ac. 

In general, if we have a number or variable in front of a parenthesis, this means that each term in the 
parenthesis is multiplied by the expression in front of the parenthesis. 

a(b -\-c-\-d-\-e-\-f-\-...) = ab + ac + ad + ae + af + . . . The "..." means "and so on." 

Example 2: Multiply 2x 3 y(-3x 4 y 2 + 2x 3 y - Wx 2 + 7x + 9). 

Solution: 

2x 3 y(-3x 4 y 2 + 2x 3 y - IOjc 2 + 7x + 9) 

= (2x 3 y)(-3x 4 y 2 ) + (2x 3 y)(2x 3 y) + (2x 3 y)(-10x 2 ) + (2x 3 y)(7x) + (2x 3 y)(9) 
= -6jcV + 4x 6 y 2 - 20;c 5 y + 14x 4 y + 18;c 3 y 

Multiplying a Polynomial by a Binomial 

A binomial is a polynomial with two terms. The Distributive Property also applies for multiplying bino- 
mials. Let's think of the first parentheses as one term. The Distributive Property says that the term in 
front of the parentheses multiplies with each term inside the parentheses separately. Then, we add the 
results of the products. 

(a + b) (c + d) = (a + b) • c + (a + b) • d Let's rewrite this answer as c • (a + b) + d • (a + b) 

We see that we can apply the Distributive Property on each of the parentheses in turn. 

c - (a + b) + d - {a + b) — c-a + c-b + d-a + d-b (or ca + cb + da + db) 

What you should notice is that when multiplying any two polynomials, every term in one polynomial 
is multiplied by every term in the other polynomial. 

Example: Multiply and simplify (2x + 1)(jc + 3). 

Solution: We must multiply each term in the first polynomial with each term in the second polynomial. 
First, multiply the first term in the first parentheses by all the terms in the second parentheses. 

(2x + 1 )(x + 3) = (2x)(x) + (2x)(3) + . . 

Now we multiply the second term in the first parentheses by all terms in the second parentheses and add 
them to the previous terms. 

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(2x + lXj + 3) = (Zx)(x) + (2x)(3) + ( 1 )(*) + ( 1 )(3) 

Now we can simplify. 

(2jc)(jc) + (2jc)(3) + (1)(jc) + (1)(3) = 2x 2 + 6x + x + 3 

= 2jc 2 + 7x + 3 

Multimedia Link: For further help, visit http://www.purplemath.com/modules/polydefs.htm - Pur- 
plemath's website - or watch this CK-12 Basic Algebra: Adding and Subtracting Polynomials YouTube 




Video 



Figure 9.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/791 

video. 

Example 3: Multiply and simplify (4x - 5)(x - 20). 

Solution: 

(4jc)(jc) + (4jc)(-20) + (-5)(jc) + (-5) (-20) = 4jc 2 - 80jc - 5x + 100 

= 4x 2 - 85jc + 100 

Solving Real- World Problems Using Multiplication of Polynomi- 
als 

We can use multiplication to find the area and volume of geometric shapes. Look at these examples. 
Example 4: Find the area of the following figure. 




Solution: We use the formula for the area of a rectangle: Area = length • width. For the big rectangle: 

Length = 5 + 3, Width = B + 2 
Area= (£ + 3)(£ + 2) 
= B 2 + 2B + W + 6 
= B 2 + 5B + 6 



347 



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Example 5: Find the volume of the following figure. 



2x+ 1 



/" A 



x + 2 

Solution: 

The volume of this shape = {area of the base) • {height). 
Area of the base = x(x + 2) 
= x 2 + 2x 

Volume = {area of base) X height 
Volume = {x 2 + 2x)(2x + 1) 

You are asked to finish this example in the practice questions. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Multiplication of Polynomials (9:49) 




Figure 9.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/792 



Multiply the following monomials. 



1. (2jc)(-7jc) 

2. 4(-6a) 

3. {-5a 2 b){-12a 3 b 3 ) 

4. {-5x){5y) 

5. y{xy A ) 

6. {3xy 2 z 2 ){15x 2 yz 3 ) 

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348 



Multiply and simplify. 



7. x 8 (x.y 3 + 3x) 

8. 2x(4x-5) 

9. 6ab(-Wa 2 b 3 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 



+ c° 



9x 3 (3x 2 -2x + 7) 

-3a 2 £(9a 2 - 4ft 2 ) 
jc-2)(jc + 3) 
a + 2)(2a)(a-3) 
-4xy)(2xV-3' 4 z 9 ) 
x-3)(x + 2) 
a 2 + 2)(3a 2 -4) 
7jc-2)(9jc-5) 
2x-l)(2x 2 -x + 3) 
3x + 2)(9x 2 -6x + 4) 
a 2 + 2a-3)(a 2 -3a + 4) 
3m + l)(m-4)(m + 5) 



22. Finish the volume example from Example 5 of the lesson. Volume = (x + 2x)(2x + 1 



Find the areas of the following figures. 




x 



3x 



Find the volumes of the following figures. 



25. 



















% 



x+ 1 



3x + 4 



349 



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26. 




2x + 4 
Mixed Review 

27. Give an example of a fourth degree trinomial in the variable n. 

28. Find the next four terms of the sequence 1, |, |, ^, . . . 

29. Reece reads three books per week. 

(a) Make a table of values for weeks zero through six. 

(b) Fit a model to this data. 

(c) When will Reece have read 63 books? 

30. Write 0.062% as a decimal. 

31. Evaluate abut + |j when a = 4 and b = -3. 

32. Solve for s: 3s(3 + 6s) + 6(5 + 3s) = 21s. 

9.3 Special Products of Polynomials 

When we multiply two linear (degree of 1) binomials, we create a quadratic (degree of 2) polynomial with 
four terms. The middle terms are like terms so we can combine them and simplify to get a quadratic or 2 nd 
degree trinomial (polynomial with three terms). In this lesson, we will talk about some special products 
of binomials. 

Finding the Square of a Binomial 

A special binomial product is the square of a binomial. Consider the following multiplication: (x+4)(x+ 
4). We are multiplying the same expression by itself, which means that we are squaring the expression. 
This means that: 

(jc + 4)(x + 4) = (jc + 4) 2 

(jc + 4)(jc + 4) = x 2 + 4x + 4x + 16 = x 2 + 8x + 16 

This follows the general pattern of the following rule. 

Square of a Binomial: (a + b) 2 = a 2 + 2ab + b 2 , and (a - b) 2 = a 2 - 2ab + b 2 

Stay aware of the common mistake (a + b) 2 = a 2 + b 2 . To see why {a + b) 2 ± a 2 + /? 2 , try substituting 
numbers for a and b into the equation (for example, a = 4 and b = 3), and you will see that it is not a 
true statement. The middle term, 2ab, is needed to make the equation work. 

Example 1: Simplify by multiplying: (x+ 10) 2 . 

Solution: Use the square of a binomial formula, substituting a = x and b = 10 

(a + b) 2 = a 2 + 2ab + b 2 
(jc + 10) 2 = (x) 2 + 2(jc)(10) + (10) 2 = x 2 + 20;t + 100 



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350 



Finding the Product of Binomials Using Sum and Difference Pat- 
terns 

Another special binomial product is the product of a sum and a difference of terms. For example, let's 
multiply the following binomials. 

(jc + 4)(jc - 4) = x 2 - 4jc + 4jc - 16 
= x 2 - 16 

Notice that the middle terms are opposites of each other, so they cancel out when we collect like terms. 
This always happens when we multiply a sum and difference of the same terms. 

(a + b)(a- b) = a - ab + ab - b 

2 / 2 

= a -b 

When multiplying a sum and difference of the same two terms, the middle terms cancel out. We get the 
square of the first term minus the square of the second term. You should remember this formula. 

Sum and Difference Formula: (a + b)(a - b) = a 2 - b 2 

Example 2: Multiply the following binomias and simplify. 

(5x + 9)(5x-9) 

Solution: Use the above formula, substituting a = 5x and b = 9. Multiply. 

(5jc + 9)(5jc - 9) = (5x) 2 - (9) 2 = 25jc 2 - 81 

Solving Real- World Problems Using Special Products of Polyno- 
mials 

Let's now see how special products of polynomials apply to geometry problems and to mental arithmetic. 
Look at the following example. 




Example: Find the area of the square. 
Solution: The area of the square = side X side 



Area = {a + b) (a + b) 



a 2 + 2ab + b 2 



Notice that this gives a visual explanation of the square of binomials product. 

351 www.ckl2.org 



Area of big square : {a-\-b) 2 = Area of blue square = a 2 + 2 {area of yellow) = 2ab-\-area of red square = b 2 
The next example shows how to use the special products in doing fast mental calculations. 
Example 3: Find the products of the following numbers without using a calculator. 

(a) 43 x 57 

(b) 45 2 

Solution: The key to these mental "tricks" is to rewrite each number as a sum or difference of numbers 
you know how to square easily. 

(a) Rewrite 43 = (50 - 7) and 57 = (50 + 7). 

Then 43x57= (50-7)(50 + 7) = (50) 2 - (7) 2 = 2500-49 = 2,451. 

(b) 45 2 = (40 + 5) 2 = (40) 2 + 2(40)(5) + (5) 2 = 1600 + 400 + 25 = 2, 025 

Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Special Products of Binomials (10:36) 



Video 



Figure 9.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/793 

Use the special product for squaring binomials to multiply these expressions. 



1. 


(x + 9) 2 


2. 


(x-1) 2 


3. 


(2j + 6) 2 


4. 


(3jc - 7) 2 


5. 


(7c + 8) 2 


6. 


(9a 2 + 6) 2 


7. 


(b 2 - l) 2 


8. 


(m 3 + 4) 2 


9. 


(i'+tf 


10. 


(6£-3) 2 


11. 


(a 3 - 7) 2 


12. 


(4x 2 +y 2 ) 2 


13. 


(8x-3) 2 



Use the special product of a sum and difference to multiply these expressions. 



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352 



14. (2x-l)(2x + l) 

15. (2x-3)(2x + 3) 

16. (4 + 6x)(4-6x) 

17. (6 + 2r)(6-2r) 

18. (-2f + 7)(2f + 7) 

19. (8z-8)(8z + 8) 

20. (3x 2 + 2)(3x 2 -2) 

21. (x-12)(x+12) 

22. (5a-2b)(5a + 2b) 

23. (ab-\)(ab + \) 

Find the area of the orange square in the following figure. It is the lower right shaded box. 
24. 




Multiply the following numbers using the special products. 

25. 45x55 

26. 97x83 

27. 19 2 

28. 56 2 

29. 876x824 

30. 1002x998 

31. 36x44 

Mixed Review 

32. Simplify 5x(3x + 5) + ll(-7-x). 

33. Cal High School has grades nine through twelve. Of the school's student population, \ are freshmen, 
f are sophomores, g are juniors, and 130 are seniors. To the nearest whole person, how many students 
are in the sophomore class? 

34. Kerrie is working at a toy store and must organize 12 bears on a shelf. In how many ways can this 
be done? 

35. Find the slope between ( |, 1] and ( |, -16). 

36. If 1 lb = 454 grams, how many kilograms does a 260-pound person weigh? 

37. Solve for v: |16 - v| = 3. 

38. Is v = x 4 + 3x 2 + 2 a function? Use the definition of a function to explain. 

9.4 Polynomial Equations in Factored Form 

We have been multiplying polynomials by using the Distributive Property where all the terms in one 
polynomial must be multiplied by all terms in the other polynomial. In this lesson, you will start learning 
how to do this process using a different method called factoring. 

353 www.ckl2.org 



Factoring: Take the factors that are common to all the terms in a polynomial. Then multiply the common 
factors by a parenthetical expression containing all the terms that are left over when you divide out the 
common factors. 




Let's look at the areas of the rectangles again: Area = length x width. The total area of the figure on the 
right can be found in two ways. 

Method 1: Find the areas of all the small rectangles and add them. 

Blue rectangle = ab 

Orange rectangle = ac 

Red rectangle = ad 

Green rectangle = ae 

Purple rectangle = 2a 

Total area = ab + ac + ad + ae + 2a 

Method 2: Find the area of the big rectangle all at once. 

Length = a 

Width = b + c + d + e + 2 
Area = a(b + c + d + e = 2) 

The answers are the same no matter which method you use: 

ab + ac + ad + ae + 2a = a(b -\-c-\-d-\-e-\-2) 



Using the Zero Product Property 

Polynomials can be written in expanded form or in factored form. Expanded form means that you 
have sums and differences of different terms: 

6x 4 + 7x 3 - 26x 2 - 17* + 30 

Notice that the degree of the polynomial is four. 

The factored form of a polynomial means it is written as a product of its factors. 

The factors are also polynomials, usually of lower degree. Here is the same polynomial in factored form. 



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354 



(jc-1)(x + 2)(2x-3)(3jc + 5) 

Suppose we want to know where the polynomial 6x 4 + 7x 3 - 26x 2 - 17x + 30 equals zero. It is quite difficult 
to solve this using the methods we already know. However, we can use the Zero Product Property to help. 

Zero Product Property: The only way a product is zero is if one or both of the terms are zero. 

By setting the factored form of the polynomial equal to zero and using this property, we can easily solve 
the original polynomial. 

- l)(x + 2) (2* - 3)(3jc + 5) = 

According to the property, for the original polynomial to equal zero, we have to set each term equal to 
zero and solve. 

(jc-1)=0->jc=1 

(jc + 2) = -> x = -2 

3 

(2x - 3) = -> x = - 

(3x + 5) = 0^ x = -- 
o 

The solutions to 6x 4 + 7x 3 - 2Qx 2 - 17* + 30 = are x = -2, -§, 1, §. 

Multimedia Link: For further explanation of the Zero Product Property, watch this CK-12 Basic Algebra: 
Zero Product Property - YouTube video. 




Figure 9.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/794 

Example 2: Solve (x - 9)(3jc + 4) = 0. 

Solution: Separate the factors using the Zero Product Property: (jc - 9)(3jc + 4) = 0. 



x-9 = 
x = 9 



or 



3x + 4 = 

3x=-4 

-4 

Y 



X = 



Finding the Greatest Common Monomial Factor 

Once we get a polynomial in factored form, it is easier to solve the polynomial equation. But first, we 
need to learn how to factor. Factoring can take several steps because we want to factor completely so we 
cannot factor any more. 



355 



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A common factor can be a number, a variable, or a combination of numbers and variables that appear 
in every term of the polynomial. 

When a common factor is factored from a polynomial, you divide each term by the common factor. What 
is left over remains in parentheses. 

Example 3: Factor: 

1. 15jc- 25 

2. 3a + 9b + 6 

Solution: 

1. We see that the factor of 5 divides evenly from all terms. 

15x-25 = 5(3x-5) 

2. We see that the factor of 3 divides evenly from all terms. 

3a + 9b + 6 = 3(a + 3b + 2) 

Now we will use examples where different powers can be factored and there is more than one common 
factor. 

Example 4: Find the greatest common factor. 

(a) a 3 - 3a 2 + 4a 

(b) 5x 3 y - 15x 2 y 2 + 25xy 3 
Solution: 

(a) Notice that the factor a appears in all terms of a 3 - 3a 2 + 4a but each term has a different power of a. 
The common factor is the lowest power that appears in the expression. In this case the factor is a. 

Let's rewrite a 3 - 3a 2 + 4a = a{a 2 ) + a{-3a) + a{4) 

Factor a to get a {a 2 - 3a + 4) 

(b) The common factors are 5xy. 

When we factor 5xy, we obtain 5xy(x 2 - 3xy + 5y 2 ). 

Solving Simple Polynomial Equations by Factoring 

We already saw how we can use the Zero Product Property to solve polynomials in factored form. Here 
you will learn how to solve polynomials in expanded form. These are the steps for this process. 

Step 1: Rewrite the equation in standard form such that: Polynomial expression = 0. 

Step 2: Factor the polynomial completely. 

Step 3: Use the zero-product rule to set each factor equal to zero. 

Step 4: Solve each equation from step 3. 

Step 5: Check your answers by substituting your solutions into the original equation. 

Example 5: Solve the following polynomial equation. 

x 2 - 2x = 
www.ckl2.org 356 



Solution: x 2 - 2x = 

Rewrite: This is not necessary since the equation is in the correct form. 
Factor: The common factor is jc, so this factors as: x(x - 2) = 0. 
Set each factor equal to zero. 







or 



Solve: 



or 



x = 2 



Check: Substitute each solution back into the original equation. 



x = 
x = 2 



(0) 2 -2(0) = 
(2) 2 -2(2) = 



Answer x = 0, x = 2 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Polynomial Equations in Factored Form (9:29) 




Figure 9.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/797 



1. What is the Zero Product Property? How does this simplify solving complex polynomials? 
Factor the common factor from the following polynomials. 

2. 36a 2 + 9a 3 -6a 7 

3. yx 3 y 2 + Ylx + lGy 

4. 3jc 3 -21jc 

5. 5jc 6 + 15x 4 

6. 4jc 3 + Wx 2 - 2x 

7. -10x 6 + 12jc 5 -4x 4 



357 



www.ckl2.org 



8. 12xy + 24xy 2 + 36xy 3 

9. 5a 3 - la 

10. 45j 12 + 30y 10 

11. 16xy 2 z + 4x 3 ;y 

Why can't the Zero Product Property be used to solve the following polynomials? 

12. (x-2)(x) = 2 

13. (x + 6) + (3x-l) = 

14. (x" 3 )(x + 7) = 

15. (x + 9)-(6x-l) = 4 

16. (x 4 )(x 2 -l) = 

Solve the following polynomial equations. 

17. x(x+12) = 

18. (2x + 3)(5x-4) = 

19. (2x+l)(2x-l) = 

20. 24x 2 -4x = 

21. 60m = 45m 2 

22. (x-5)(2x + 7)(3x-4) = 

23. 2x(x + 9)(7x-20) = 

24. 18v - 3y 2 = 

25. 9x 2 = 27x 

26. 4a 2 + a = 

27. & 2 -i = 

Mixed Review 

28. Rewrite in standard form: -Ax + llx 4 - 6x 7 + 1 - 3x 2 . State the polynomial's degree and leading 
coefficient. 

29. Simplify (9a 2 - 8a + 11a 3 ) - (3a 2 + 14a 5 - 12a) + (9 - 3a 5 - 13a). 

30. Multiply la 3 by (36a 4 + 6). 

31. Melissa made a trail mix by combining x ounces of a 40% cashew mixture with y ounces of a 30% 
cashew mixture. The result is 12 ounces of cashews. 

(a) Write the equation to represent this situation. 

(b) Graph using its intercepts. 

(c) Give three possible combinations to make this sentence true. 

32. Explain how to use mental math to simplify 8(12.99). 

9.5 Factoring Quadratic Expressions 

In this lesson, we will learn how to factor quadratic polynomials for different values of a, /?, and c. In 
the last lesson, we factored common monomials, so you already know how to factor quadratic polynomials 
where c = 0. 

www.ckl2.org 358 



Factoring Quadratic Expressions in Standard From 

Quadratic polynomials are polynomials of degree 2. The standard form of a quadratic polynomial is 
ax 2 + bx + c, where a, b, and c are real numbers. 

Example 1: Factor x 2 + 5x + 6. 

Solution: We are looking for an answer that is a product of two binomials in parentheses: (x+ )(■*+ 

)• 

To fill in the blanks, we want two numbers m and n that multiply to 6 and add to 5. A good strategy is 
to list the possible ways we can multiply two numbers to give us 6 and then see which of these pairs of 
numbers add to 5. The number six can be written as the product of. 

6 = 1x6 and 1 + 6 = 7 
6 = 2x3 and 2 + 3 = 5 

So the answer is (x + 2){x + 3). 

We can check to see if this is correct by multiplying (x + 2)(x + 3). 

x is multiplied by x and 3 = x 2 + 3x. 

2 is multiplied by x and 3 = 2x + 6. 

Combine the like terms: x 2 + 5x + 6. 

Example 2: Factor x 2 - 6x + 8. 

Solution: We are looking for an answer that is a product of the two parentheses (jc+ )(■*+ )• 

The number 8 can be written as the product of the following numbers. 
8 = 1-8 and 1 + 8 = 9 Notice that these are two different choices. 

8 = (-l)(-8) and - 1 + (-8) = -9 

8 = 2x4 and 2 + 4 = 6 

And 

8 = (-2) • (-4) and -2 + (-4) = -6 <- This is the correct choice. 

The answer is (x - 2)(x - 4). 

Example 3: Factor x 2 + 2x - 15. 

Solution: We are looking for an answer that is a product of two parentheses (x ± )(x ± ). 

In this case, we must take the negative sign into account. The number -15 can be written as the product 
of the following numbers. 

-15 = -1 • 15 and -1 + 15 = 14 Notice that these are two different choices. 

And also, 

-15 = 1 • (-15) and 1 + (-15) = -14 Notice that these are two different choices. 

-15 = (-3) x 5 and (-3) + 5 = 2 This is the correct choice. 

-15 = 3 x (-5) and 3 + (-5) = -2 

The answer is (x - 3)(x + 5). 

Example 4: Factor -x 2 + x + 6. 

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Solution: First factor the common factor of -1 from each term in the trinomial. Factoring -1 changes the 
signs of each term in the expression. 

-x 2 + x + 6 = -{x 2 - x - 6) 

We are looking for an answer that is a product of two parentheses {x ± )(x ± ). 

Now our job is to factor x 2 - x - 6. 

The number -6 can be written as the product of the following numbers. 

-6 = (-l)x6 and (-1) + 6 = 5 

- 6 = 1 x (-6) and 1 + (-6) = -5 

- 6 = (-2) x 3 and (-2) + 3 = 1 

- 6 = 2 X (-3) and 2 + (-3) = -1 This is the correct choice. 

The answer is -(jc - 3)(x + 2). 
To Summarize: 

A quadratic of the form x 2 + bx + c factors as a product of two parenthesis (jc + m){x + ri). 

• lib and c are positive then both m and n are positive. 

— Example x 2 + 8x + 12 factors as (jc + 6)(jc + 2). 

• If b is negative and c is positive then both m and n are negative. 

— Example x 2 - 6x + 8 factors as (jc - 2)(x - 4). 

• If c is negative then either m is positive and n is negative or vice- versa. 

— Example x 2 + 2x - 15 factors as (jc + 5)(x - 3). 

— Example x 2 + 34x - 35 factors as (jc + 35) (jc - 1). 

• If a — — 1, factor a common factor of -1 from each term in the trinomial and then factor as usual. 
The answer will have the form — (jc + m){x + n). 

— Example -x 2 + x + 6 factors as -(jc - 3)(jc + 2). 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Factoring Quadratic Equations (16:30) 

Factor the following quadratic polynomials. 

1. jc 2 + 10jc + 9 

2. jc 2 + 15jk+50 

3. jc 2 + 10jc+21 

4. jc 2 + 16jc + 48 

5. jc 2 -11jc + 24 

6. jc 2 -13x + 42 

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Figure 9.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/798 

7. x 2 - 14* + 33 

8. x 2 -9x + 20 

9. x 2 + 5x-14 

10. x 2 + 6x-27 

11. x 2 + 7x-78 

12. x 2 + 4x-32 

13. x 2 -12x-45 

14. x 2 -5x-50 

15. x 2 -3x-40 

16. x 2 -x-56 

17. -x 2 -2x-l 

18. -x 2 -5x + 24 

19. -x 2 + 18x-72 

20. -x 2 + 25x-150 

21. x 2 + 21x+108 

22. -x 2 + llx-30 

23. x 2 + 12x-64 

24. x 2 -17x-60 

Mixed Review 

25. Evaluate /(2) when /(x) = ^x 2 - 6x + 4. 

26. The Nebraska Department of Roads collected the following data regarding mobile phone distractions 
in traffic crashes by teen drivers. 

(a) Plot the data as a scatter plot. 

(b) Fit a line to this data. 

(c) Predict the number of teenage traffic accidents attributable to cell phones in the year 2012. 

Table 9.1: 



Year (y) 



Total (n) 



2002 
2003 
2004 
2005 
2006 
2007 



41 
43 
47 
38 
36 
40 



361 



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Table 9.1: (continued) 



Year (y) Total (n) 



2008 42 

2009 42 



27. Simplify V405. 

28. Graph the following on a number line: -n, V2, |, — jq, Vl6. 

29. What is the multiplicative inverse of |? 

Quick Quiz 

1. Name the following polynomial. State its degree and leading coefficient 6x 2 y 4 z + Qx 6 - 2y 5 + llxyz 4 . 

2. Simplify (a 2 b 2 c + lla/?c 5 ) + (Aabc 5 - 3a 2 b 2 c + 9abc). 

3. A rectangular solid has dimensions (a + 2) by (a + 4) by (3a). Find its volume. 

4. Simplify -3hjk 3 (h 2 fk + 6M 2 ). 

5. Find the solutions to (jc - 3)(x + 4)(2jc - 1) = 0. 

6. Multiply (a - 9fe)(a + 96). 

9.6 Factoring Special Products 

When we learned how to multiply binomials, we talked about two special products: the Sum and Difference 
Formula and the Square of a Binomial Formula. In this lesson, we will learn how to recognize and factor 
these special products. 

Factoring the Difference of Two Squares 

We use the Sum and Difference Formula to factor a difference of two squares. A difference of two squares 
can be a quadratic polynomial in this form: a 2 - b 2 . Both terms in the polynomial are perfect squares. In 
a case like this, the polynomial factors into the sum and difference of the square root of each term. 

a 2 -b 2 = (a + b)(a-b) 

In these problems, the key is figuring out what the a and b terms are. Let's do some examples of this type. 
Example 1: Factor the difference of squares. 

(a) x 2 - 9 

(b) x 2 y 2 - 1 
Solution: 

(a) Rewrite as x 2 - 9 as x 2 - 3 2 . Now it is obvious that it is a difference of squares. 
We substitute the values of a and b for the Sum and Difference Formula: 

+ 3)0-3) 

The answer is x 2 - 9 = (jc + 3)(jc - 3). 

(b) Rewrite as x 2 y 2 - 1 as (xy) 2 - l 2 . This factors as (xy + l)(xy - 1). 

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Factoring Perfect Square Trinomials 

A perfect square trinomial has the form 

a 2 + 2ab + b 2 or a 2 - 2ab + b 2 

The factored form of a perfect square trinomial has the form 

{a + b) 2 if a 2 + 2{ab) + b 2 
And 

(a-b) 2 if a 2 -2{ab)+b 2 

In these problems, the key is figuring out what the a and b terms are. Let's do some examples of this type. 

Example: x 2 + 8x + 16 

Solution: Check that the first term and the last term are perfect squares. 

x 2 + 8jc+16 as jc 2 + 8x + 4 2 . 

Check that the middle term is twice the product of the square roots of the first and the last terms. This 
is true also since we can rewrite them. 

x 2 + 8x + 16 as x 2 + 2 • 4 • x + 4 2 

This means we can factor x 2 + 8x + 16 as (x + 4) 2 . 

Example 2: Factor x 2 - 4x + 4. 

Solution: Rewrite x 2 - 4x + 4 as x 2 + 2 • (-2) • x + (-2) 2 . 

We notice that this is a perfect square trinomial and we can factor it as: (jc - 2) 2 . 

Solving Polynomial Equations Involving Special Products 

We have learned how to factor quadratic polynomials that are helpful in solving polynomial equations like 
ax 2 + bx + c = 0. Remember that to solve polynomials in expanded form, we use the following steps: 

Step 1: Rewrite the equation in standard form such that: Polynomial expression = 0. 

Step 2: Factor the polynomial completely. 

Step 3: Use the Zero Product Property to set each factor equal to zero. 

Step 4: Solve each equation from step 3. 

Step 5: Check your answers by substituting your solutions into the original equation. 

Example 3: Solve the following polynomial equations. 

x 2 + 7x + 6 = 

Solution: No need to rewrite because it is already in the correct form. 
Factor: We write 6 as a product of the following numbers: 

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6 = 6x1 



x 2 + 7x + 6 = 



Set each factor equal to zero: 



and 
factors as 



6 + 1 = 7 
(jc+1)(jc + 6) = 



x+1 = 



or 



x + 6 = 



Solve: 



or 



Check: Substitute each solution back into the original equation. 

(-1) 2 + 7(-l) + 6 = 1 + (-7) + 6 = 
(-6) 2 + 7(-6) + 6 = 36 + (-42) + 6 = 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Factoring Special Products (10:08) 




Figure 9.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/799 



Factor the following perfect square trinomials. 

1. x 2 + 8x+16 

2. x 2 -18x + 81 

3. -x 2 + 24x-144 

4. x 2 + 14jc + 49 

5. 4jc 2 -4x+ 1 

6. 25jc 2 + 60* + 36 

7. 4jc 2 - 12xy + 9y 2 

8. x 4 + 22x 2 + 121 

Factor the following difference of squares. 
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364 



9. x 2 -4 

10. x 2 -36 

11. -x 2 + 100 

12. x 2 -400 

13. 9x 2 -4 

14. 25x 2 -49 

15. -36x 2 + 25 

16. 16x 2 -81y 2 

Solve the following quadratic equations using factoring. 

17. x 2 -llx + 30 = 

18. x 2 + 4x = 21 

19. x 2 + 49 = 14x 

20. x 2 -64 = 

21. x 2 -24x + 144 = 

22. 4x 2 -25 = 

23. x 2 + 26x = -169 

24. -x 2 -16x-60 = 

Mixed Review 

{ 3x + 7v = 1 

25. Find the value for fc that creates an infinite number of solutions to the system < 

[kx - Uy = -2 

26. A restaurant has two kinds of rice, three choices of mein, and four kinds of sauce. How many plate 
combinations can be created if you choose one of each? 

27. Graph v - 5 = 4(x + 4). Identify its slope. 

28. $600 was deposited into an account earning 8% interest compounded annually. 

(a) Write the exponential model to represent this situation. 

(b) How much money will be in the account after six years? 

29. Divide 4 § H- -3 i. 

30. Identify an integer than is even and not a natural number. 

9.7 Factoring Polynomials Completely 

We say that a polynomial is factored completely when we factor as much as we can and we are unable to 
factor any more. Here are some suggestions that you should follow to make sure that you factor completely 

y Factor all common monomials first. 

y Identify special products such as difference of squares or the square of a binomial. Factor according to 
their formulas. 

y If there are no special products, factor using the methods we learned in the previous sections. 

y Look at each factor and see if any of these can be factored further. 

Example 1: Factor the following polynomials completely. 

(a) 2x 2 - 8 

(b) x 3 + 6x 2 + 9x 

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Solution: 

(a) Look for the common monomial factor. 2x 2 - 8 = 2{x 2 - 4). Recognize x 2 - 4 as a difference of squares. 
We factor 2{x 2 - 4) = 2{x + 2)(x - 2). If we look at each factor we see that we can't factor anything else. 
The answer is 2{x + 2){x - 2). 

(b) Recognize this as a perfect square and factor as x{x + 3) 2 . If we look at each factor we see that we 
can't factor anything else. The answer is x(x + 3) 2 . 

Factoring Common Binomials 

The first step in the factoring process is often factoring the common monomials from a polynomial. Some- 
times polynomials have common terms that are binomials. For example, consider the following expression. 

x(3x + 2)-5(3x + 2) 

You can see that the term (3x + 2) appears in both terms of the polynomial. This common term can be 
factored by writing it in front of a set of parentheses. Inside the parentheses, we write all the terms that 
are left over when we divide them by the common factor. 

(3jc + 2)(jc-5) 

This expression is now completely factored. Let's look at some examples. 
Example 2: Factor 3x(x - 1) + 4(jc - 1). 

Solution: 3x(x - 1) + 4(x - 1) has a common binomial of (x - 1). 
When we factor the common binomial, we get (x - l)(3x + 4). 

Factoring by Grouping 

It may be possible to factor a polynomial containing four or more terms by factoring common monomials 
from groups of terms. This method is called factoring by grouping. The following example illustrates 
how this process works. 

Example 3: Factor 2x + 2y + ax + ay. 

Solution: There isn't a common factor for all four terms in this example. However, there is a factor of 
2 that is common to the first two terms and there is a factor of a that is common to the last two terms. 
Factor 2 from the first two terms and factor a from the last two terms. 



2x + 2y + ax + ay = 2(x + y) + a{x + y) 



Now we notice that the binomial {x + y) is common to both terms. We factor the common binomial and 
get. 

{x + y){2 + a) 

Our polynomial is now factored completely. 

We know how to factor Quadratic Trinomials {ax 2 + bx + c) where a ^ 1 using methods we have previously 
learned. To factor a quadratic polynomial where a + 1, we follow the following steps. 

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1. We find the product ac. 

2. We look for two numbers that multiply to give ac and add to give b. 

3. We rewrite the middle term using the two numbers we just found. 

4. We factor the expression by grouping. 

Let's apply this method to the following examples. 
Example 4: Factor 3x 2 + 8x + 4 by grouping. 
Solution: Follow the steps outlined above. 

ac = 3 • 4 = 12 

The number 12 can be written as a product of two numbers in any of these ways: 

12 = 1 x 12 and 1 + 12 = 13 

12 = 2 x 6 and 2 + 6 = 8 This is the correct choice. 

Rewrite the middle term as: 8x = 2x + 6x, so the problem becomes the following. 

3x 2 + 8x + 4 = 3x 2 + 2x + 6x + 4 

Factor an x from the first two terms and 2 from the last two terms. 

x(3x + 2) + 2(3x + 2) 

Now factor the common binomial (3x + 2). 

(3x + 2)(x + 2) 

Our answer is (3x + 2)(x + 2). 

In this example, all the coefficients are positive. What happens if the b is negative? 

Example 5: Factor 6x 2 - llx + 4 by grouping. 

Solution: ac = 6 • 4 = 24 

The number 24 can be written as a product of two numbers in any of these ways. 



24 = 1 x 24 


and 


1 + 24 = 25 


24 = (-1) x (-24) 


and 


(-1) + (-24) = -25 


24 = 2 x 12 


and 


2 + 12 = 14 


24 = (-2) x (-12) 


and 


(-2) + (-12) = -14 


24 = 3 x 8 


and 


3 + 8 = 11 


24 = (-3) x (-8) 


and 


(-3) + (-8) = -11 This is the correct choice. 



Rewrite the middle term as -IIjc = -3x - 8x, so the problem becomes: 

6x 2 - 11* + 4 = 6x 2 - 3x - 8x + 4 

Factor by grouping. Factor a 3x from the first two terms and factor -4 from the last two terms. 

3x(2x-l)-4(2x-l) 

Now factor the common binomial (2x - 1). 
Our answer is (2x - 1)(3jc - 4). 

367 www.ckl2.org 



Solving Real- World Problems Using Polynomial Equations 

Now that we know most of the factoring strategies for quadratic polynomials, we can see how these methods 
apply to solving real- world problems. 

Example 6: The product of two positive numbers is 60. Find the two numbers if one of the numbers is 4 
more than the other. 

Solution: x = one of the numbers and x-\- 4 equals the other number. The product of these two numbers 
equals 60. We can write the equation. 



x( x + 4) = 60 



Write the polynomial in standard form. 



x 2 + 4x = 60 



.,2 



x A + 4x - 60 = 

Factor: -60 = 6 x (-10) and 6 + (-10) = -4 

-60 = -6 x 10 and -6 + 10 = 4 This is the correct choice. 

The expression factors as (x + 10) (x - 6) = 0. 

Solve: 

x+10 = x-6 = 

or 
x = -10 x = 6 

Since we are looking for positive numbers, the answer must be positive. 
x = 6 for one number, and x + 4 = 10 for the other number. 
Check: 6 • 10 = 60 so the answer checks. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Factor by Grouping and Factoring Completely (13:57) 

Factor completely. 

1. 2jk 2 + 16jc + 30 

2. 12c 2 -75 

3. -x 3 + 17jc 2 - 70jc 

4. 6jc 2 - 600 

5. -5/ 2 -20/-20 

6. 6;t 2 + 18;c - 24 

7. -n 2 + 10rc -21 

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Figure 9.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/800 

8. 2a 2 - Ua - 16 

9. 2jc 2 - 512 

10. 12jc 3 + 12jc 2 + 3jc 

Factor by grouping. 

11. 6x 2 - 9x + IOjc - 15 

12. 5jc 2 - 35x + jc - 7 

13. 9x 2 -9x-jc+1 

14. 4jc 2 + 32x - 5x - 40 

15. 12jc 3 -14x 2 + 42jc-49 

16. 4jc 2 + 25jc-21 

17. 24Z? 3 + 32b 2 - 3b - 4 

18. 2m 3 + 3m 2 + 4m + 6 

19. 6x 2 + 7jc+1 

20. 4jc 2 + 8jc-5 

21. 5a 3 -5a 2 + 7a -7 

22. 3jc 2 + 16x + 21 

23. 4xy + 32x + 20y + 160 

24. Wab + 40a + 6b + 24 

25. 9m?z + 12m + 3?z + 4 

26. Ajk - 8j 2 + 5Jk - 10 j 

27. 24^/7 + 64a -21b- 56 

Solve the following application problems. 

28. One leg of a right triangle is seven feet longer than the other leg. The hypotenuse is 13 feet. Find 
the dimensions of the right triangle. 

29. A rectangle has sides of x + 2 and x-1. What value of x gives an area of 108? 

30. The product of two positive numbers is 120. Find the two numbers if one numbers is seven more 
than the other. 

31. Framing Warehouse offers a picture-framing service. The cost for framing a picture is made up of 
two parts. The cost of glass is $1 per square foot. The cost of the frame is $2 per linear foot. If the 
frame is a square, what size picture can you get framed for $20.00? 

Mixed Review 



32. The area of a square varies directly with its side length. 

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(a) Write the general variation equation to model this sentence. 

(b) If the area is 16 square feet when the side length is 4 feet, find the area when s = 1.5 feet. 

33. The surface area is the total amount of surface of a three-dimensional figure. The formula for the 
surface area of a cylinder is SA = 2nr 2 + Inrh^ where r = radius and h = height of the cylinder. 
Determine the surface area of a soup can with a radius of 2 inches and a height of 5.5 inches. 

34. Factor 25g 2 - 36. Solve this polynomial when it equals zero. 

35. What is the greatest common factor of 343r 3 £, 2l£ 4 , and 63r£ 5 ? 

36. Discounts to the hockey game are given to groups with more than 12 people. 

(a) Graph this solution on a number line 

(b) What is the domain of this situation? 

(c) Will a church group with 12 members receive a discount? 

9.8 Probability of Compound Events 

We begin this lesson with a reminder of probability. 

The experimental probability is the ratio of the proposed outcome to the number of experiment trials. 

number of times the event occured 



P(success) = 



total number of trials of experiment 



Probability can be expressed as a percentage, a fraction, a decimal, or a ratio. 

This lesson will focus on compound events and the formulas used to determine the probability of such 
events. 

Compound events are two simple events taken together, usually expressed as A and B. 



Independent and Dependent Events 



Example: Suppose you flip a coin and roll a die at the same time. What is the probability you will flip a 
head and roll a four? 

These events are independent. Independent events occur when the outcome of one event does not affect 
the outcome of the second event. Rolling a four has no effect on tossing a head. 

To find the probability of two independent events, multiply the probability of the first event by the 
probability of the second event. 

P(A and B) = P(A) • P(B) 

Solution: 

P(tossing a head) = - 

P(rolling a 4) = - 

P(tossing a head AND rolling a 4) = - X - = — 

When events depend upon each other, they are called dependent events. Suppose you randomly draw a 
card from a standard deck then randomly draw a second card without replacing the first. The second 
probability is now different from the first. 

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To find the probability of two dependent events, multiply the probability of the first event by the 
probability of the second event, after the first event occurs. 

P(A and B) = P(A) • P{B following A) 

Example: Two cards are chosen from a deck of cards. What is the probability that they both will be face 
cards? 

Solution: Let A = 1st Face card chosen and B = 2nd Face card chosen. The total number of face cards in 
the deck is 4 X 3 = 12. 

HA) = - 

v ; 52 

P(B) = — , remember, one card has been removed. 
v J 51 

12 11 12 11 33 
Pi A AND B) = —x — or P(AnB) = —X — = 

v ; 52 51 v ; 52 51 663 

11 
Pi A n 5) = — 
v ; 221 

Mutually Exclusive Events 

Events that cannot happen at the same time are called mutually exclusive events. For example, a 
number cannot be both even and odd or you cannot have picked a single card from a deck of cards that is 
both a ten and a jack. Mutually inclusive events, however, can occur at the same time. For example a 
number can be both less than 5 and even or you can pick a card from a deck of cards that can be a club 
and a ten. 

When finding the probability of events occurring at the same time, there is a concept known as the "double 
counting" feature. It happens when the intersection is counted twice. 




In mutually exclusive events, P{A C\ B) = 0, because they cannot happen at the same time. 

To find the probability of either mutually exclusive events A or B occurring, use the following formula. 

To find the probability of one or the other mutually exclusive or inclusive events, add the individual 
probabilities and subtract the probability they occur at the same time. 

P(A or B) = P(A) + P(B) - P(A n B) 

Example: Two cards are drawn from a deck of cards. Let: 
A: 1 st card is a club 
B: 1 st card is a 7 

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C: 2 nd card is a heart 

Find the following probabilities: 

(a) P(A or B) 

(b) P(B or A) 

(c) P(A and C) 

Solution: 

(a) P(A or B) = If + ± - ± 
P(A orB) = § 
P(A or B) = 3§ 

(b)P(5orA) = ^ + if-^ 
P(fi or A) = If 
P(B orA) = -^ 

(c) P(A am/ C) = |f x if 
P(A and C) = ^ 
P(A anrf C) = ^ 

Practice Set 

1. Define independent events. 

Are the following events independent or dependent? 

2. Rolling a die and spinning a spinner 

3. Choosing a book from the shelf then choosing another book without replacing the first 

4. Tossing a coin six times then tossing it again 

5. Choosing a card from a deck, replacing it, and choosing another card 

6. If a die is tossed twice, what is the probability of rolling a 4 followed by a 5? 

7. Define mutually exclusive. 

Are these events mutually exclusive or mutually inclusive? 

8. Rolling an even and an odd number on one die. 

9. Rolling an even number and a multiple of three on one die. 

10. Randomly drawing one card and the result is a jack and a heart. 

11. Randomly drawing one card and the result is black and a diamond. 

12. Choosing an orange and a fruit from the basket. 

13. Choosing a vowel and a consonant from a Scrabble bag. 

14. Two cards are drawn from a deck of cards. Determine the probability of each of the following events: 

(a) P(heart or club) 

(b) P(heart and club) 

(c) P(red or heart) 

(d) P(jack or heart) 

(e) P(red or ten) 

(f) P(red queen or black jack) 

15. A box contains 5 purple and 8 yellow marbles. What is the probability of successfully drawing, in 
order, a purple marble and then a yellow marble? {Hint: In order means they are not replaced.} 

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16. A bag contains 4 yellow, 5 red, and 6 blue marbles. What is the probability of drawing, in order, 2 
red, 1 blue, and 2 yellow marbles? 

17. A card is chosen at random. What is the probability that the card is black and is a 7? 

Mixed Review 

18. A circle is inscribed within a square, meaning the circle's diameter is equal to the square's side length. 
The length of the square is 16 centimeters. Suppose you randomly threw a dart at the figure. What 
is the probability the dart will land in the square, but not in the circle? 

19. Why is 7 - 14x 4 + 7xy 5 - lx~ l = 8x 2 y 3 not considered a polynomial? 

20. Factor 72b 5 m 3 w 9 - 6(bm) 2 w 6 . 

21. Simplify 2 5 - 7 3 a 3 b 7 + 3^a 3 b 7 - 2 3 . 

22. Bleach breaks down cotton at a rate of 0.125% with each application. A shirt is 100% cotton. 

(a) Write the equation to represent the percentage of cotton remaining after w washes. 

(b) What percentage remains after 11 washes? 

(c) After how many washes will 75% be remaining? 

23. Evaluate 9 _ 2x3+22 ; ■ 

9.9 Chapter 9 Review 

Define the following words: 

1. Polynomial 

2. Monomial 

3. Trinomial 

4. Binomial 

5. Coefficient 

6. Independent events 

7. Factors 

8. Factoring 

9. Greatest common factor 

10. Constant 

11. Mutually exclusive 

12. Dependent events 

Identify the coefficients, constants, and the polynomial degrees in each of the following polynomials. 

13. x 5 -3x 3 + 4jc 2 -5x + 7 

14. x A - 3x 3 y 2 + 8jc - 12 

Rewrite the following in standard form. 

15. -4/7 + 4 + b 2 

16. 3x 2 + 5jc 4 -2x + 9 

Add or subtract the following polynomials and simplify. 

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17. Add x 2 - 2xy + y 2 and 2y 2 - 4x 2 and lOxy + y 3 . 

18. Subtract x 3 - 3x 2 + 8jc + 12 from 4x 2 + 5x - 9. 

19. Add 2x 3 + 3x 2 y + 2y and x 3 - 2x 2 y + 3y 

Multiply and simplify the following polynomials. 

20. (-3y 4 )(2y 2 ) 

21. -7a 2 £c 3 (5a 2 -36 2 -9c 2 ) 

22. -7y(4y 2 - 2y + 1) 

23. (3x 2 + 2x-5)(2x-3) 

24. (x 2 -9)(4x 4 + 5x 2 -2) 

25. (2x 3 + 7)(2x 3 -7) 

Square the binomials and simplify. 

26. (x 2 + 4) 2 

27. (5x-2y) 2 

28. (13x 2 + 2y) 

Solve the following polynomial equations. 

29. 4x(x + 6)(4x-9) = 

30. x(5x - 4) = 

Factor out the greatest common factor of each expression 

31. -12n + 28rc + 4 

32. 45x 10 + 45x 7 + 18x 4 

33. -16y 5 - 8y 5 x 2 + 40y 6 x 3 

34. 15m 4 - 10m 6 - 10w 3 v 

35. -6a 9 + 20a 4 b + 10a 3 

36. 12x + 27y 2 - 27x 6 

Factor the difference of squares. 

37. x 2 -100 

38. x 2 -l 

39. 16x 2 -25 

40. 4x 2 -81 

Factor the following expressions completely. 

41. 5« 2 + 25n 

42. 7r 2 + 37r + 36 

43. 4v 2 + 36v 

44. 336xy - 288x 2 + 294y - 252x 

45. lOxy - 25x + 8y - 20 

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Complete the following problems. 

46. One leg of a right triangle is 3 feet longer than the other leg. The hypotenuse is 15 feet. Find the 
dimensions of the right triangle. 

47. A rectangle has sides of x + 5 and x - 3. What value of x gives an area of 48? 

48. Are these two events mutually exclusive, mutually inclusive, or neither? "Choosing the sports section 
from a newspaper" and "choosing the times list for the movie theatre" 

49. You spin a spinner with seven equal sections numbered one through seven and roll a six-sided cube. 
What is the probability that you roll a five on both the cube and the spinner? 

50. You spin a spinner with seven equal sections numbered one through seven and roll a six-sided cube. 
Are these eventually mutually exclusive? 

51. You spin a spinner with seven equal sections numbered one through seven and roll a six-sided cube. 
Are these events independent? 

52. You spin a spinner with seven equal sections numbered one through seven and roll a six-sided cube. 
What is the probability you spin a 3, 4, or 5 on the spinner or roll a 2 on the cube? 

9.10 Chapter 9 Test 

Simplify the following expressions. 

1. (4x 2 + 5x+l)-(2x 2 -x-3) 

2. (2x + 5) - (x 2 + 3x - 4) 

3. (b + Ac) + (6b + 2c + 3d) 

4. (5x 2 + 3x + 3) + (3x 2 - 6x + 4) 

5. (3x + 4)(x-5) 

6. (9x 2 + 2)(x-3) 

7. (4x + 3)(8x 2 + 2x + 7) 

Factor the following expressions. 

8. 27x 2 -18x + 3 

9. 9« 2 -100 

10. 648x 2 -32 

11. 8lp 2 -90p + 25 

12. 6x 2 -35x + 49 

Solve the following problems. 

13. A rectangle has sides of x + 7 and x - 5. What value of x gives an area of 63? 

14. The product of two positive numbers is 50. Find the two numbers if one of the numbers is 6 more 
than the other. 

15. Give an example of two independent events. Determine the probability of each event. Use it to find: 

(a) P(AUB) 

(b) P{ADB) 

16. The probability it will rain on any given day in Seattle is 45%. Find the probability that: 

(a) It will rain three days in a row. 

(b) It will rain one day, not the next, and rain again on the third day. 

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Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/flexr/chapter/9619. 



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Chapter 10 

Quadratic Equations and 
Functions 



As you saw in Chapter 8, algebraic functions not only produce straight lines but curved ones too. A special 
type of curved function is called a parabola. Perhaps you have seen the shape of a parabola before: 

• The shape of the water from a drinking fountain 

• The path a football takes when thrown 

• The shape of an exploding firework 

• The shape of a satellite dish 

• The path a diver takes into the water 

• The shape of a mirror in a car's headlamp 

Many real life situations model a quadratic equation. This chapter will explore the graph of a quadratic 
equation and how to solve such equations using various methods. 




10.1 Graphs of Quadratic Functions 

Chapter 9 introduced the concept of factoring quadratic trinomials of the form = ax 2 + bx + c. This is 
also called the standard form for a quadratic equation. The most basic quadratic equation is y = x 2 . 

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The word quadratic comes from the Latin word quadrare, meaning "to square." By creating a table of 
values and graphing the ordered pairs, you find that a quadratic equation makes a {/-shaped figure called 
a parabola. 

Table 10.1: 




1 
2 



4 

1 

1 
4 






The Anatomy of a Parabola 



A parabola can be divided in half by a vertical line. Because of this, parabolas have symmetry. The 
vertical line dividing the parabola into two equal portions is called the line of symmetry. All parabolas 
have a vertex, the ordered pair that represents the bottom (or the top) of the curve. 

The vertex of a parabola has an ordered pair (h, k) . 



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378 



Line of 
symmetry 





»- 


■ 






/ 


/ 










1 ' " 

6- 
5- 

1 A 






/ 














































*\ r 




















<7 






















1 « 
























\ 














X 


i -- 


»1 - 








\M 5 6 - 


r i 


s 




"1 
-2r 






/ 


•V€ 


rte 


K 





x-intercepts 

Because the line of symmetry is a vertical line, its equation has the form y = /z, where h = the x- coordinate 
of the vertex. 

An equation of the form y = ax 2 forms a parabola. 

If a is positive, the parabola will open upward. The vertex will be a minimum. 

If a is negative, the parabola will open downward. The vertex will be a maximum. 

The variable a in the equation above is called the leading coefficient of the quadratic equation. Not only 
will it tell you if the parabola opens up or down, but it will also tell you the width. 

Iffl>lorfl<— 1, the parabola will be narrow about the line of symmetry. 

If -1 < a < 1, the parabola will be wide about the line of symmetry. 

Example 1: Determine the direction and shape of the parabola formed by y = - 2 „ 

Solution: The value of a in the quadratic equation is -1. 



\x\ 



Because a is negative, the parabola opens downward. 

Because a is between -1 and 1, the parabola is wide about its line of symmetry. 



Domain and Range 

Several times throughout this textbook, you have experienced the terms domain and range. Remember: 

• Domain is the set of all inputs (x-coordinates). 

• Range is the set of all outputs (y-coordinates). 



The domain of every quadratic equation is all real numbers (R). The range of a parabola depends upon 
whether the parabola opens up or down. 

If a is positive, the range will be y > k. 

If a is negative, the range will be y < k, where k = y— coordinate of the vertex. 



379 



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Vertical Shifts 

Compare the five parabolas to the right. What do you notice? 

1 




y=x 
y=x 2 + l 
y = x J =1 

y = x 2 +2 
y =x -2 



The five different parabolas are congruent with different y-intercepts. Each parabola has an equation of 
the form y = ax 2 + c, where a = 1 and c = y-intercept. In general, the value of c will tell you where the 
parabola will intersect the y-axis. 

The equation y = ax 2 + c is a parabola with a y-intercept of (0, c). 

The vertical movement along a parabola's line of symmetry is called a vertical shift. 

Example 1: Determine the direction, shape, and y-intercept of the parabola formed by y 



3^2 



4. 



Solution: The value of a in the quadratic equation is 



2' 



• Because a is positive, the parabola opens upward. 

• Because a is greater than 1, the parabola is narrow about its line of symmetry. 

• The value of c is -4, so the y-intercept is (0, -4). 

Projectiles are often described by quadratic equations. When an object is dropped from a tall building or 
cliff, it does not travel at a constant speed. The longer it travels, the faster it goes. Galileo described this 
relationship between distance fallen and time. It is known as his kinematical law. It states the "distance 
traveled varies directly with the square of time." As an algebraic equation, this law is: 

d = Wt 2 

Use this information to graph the distance an object travels during the first six seconds. 

Table 10.2: 




1 
2 
3 

4 

5 
6 





16 

64 

144 

256 

400 

576 



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380 



1000 


































































/ + 




























































The parabola opens upward and its vertex is located at the origin. The value of a > 1, so the graph is 
narrow about its line of symmetry. However, because the values of the dependent variable d are very large, 
the graph is misleading. 

Example 2: Anne is playing golf. On the fourth tee, she hits a slow shot down the level fairway. The ball 
follows a parabolic path described by the equation, y = x - 0.04x 2 , where x = distance in feet from the tee 
and y = height of the golf ball, in feet. 

Describe the shape of this parabola. What is its y- intercept? 

Solution: The value of a in the quadratic equation is -0.04. 

• Because a is negative, the parabola opens downward. 

• Because a is between -1 and 1, the parabola is wide about its line of symmetry. 

• The value of c is 0, so the y-intercept is (0, 0). 

The distance it takes a car to stop (in feet) given its speed (in miles per hour) is given by the function 
d(s) = ^ s 2 + s. This equation is in standard form f(x) = ax 2 + bx + c, where a = 4j,& = 1, and c = 0. 

Graph the function by making a table of speed values. 



400 












/ 


200 










































Table 10.3: 





10 

20 





15 

40 



381 



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Table 10.3: (continued) 



30 
40 
50 
60 



75 
120 
175 
240 



• The parabola opens upward with a vertex at (0, 0). 

• The line of symmetry is x — 0. 

• The parabola is wide about its line of symmetry. 

Using the function to find the stopping distance of a car travelling 65 miles per hour yields: 

</(65) = — (65) 2 + 65 = 276.25 feet 

Multimedia Link: For more information regarding stopping distance, watch this CK-12 Basic Algebra: 
Algebra Applications: Quadratic Functions - YouTube video. 




Figure 10.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/258 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 



CK-12 Basic Algebra: Graphs of Quadratic Functions (16:05) 



1. Define the following terms in your own words. 

(a) Vertex 

(b) Line of symmetry 

(c) Parabola 

(d) Minimum 

(e) Maximum 

2. Without graphing, how can you tell if y = ax 2 + bx + c opens up or down? 

3. Using the parabola below, identify the following: 



www.ckl2.org 



382 




Figure 10.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/801 



(a) Vertex 

(b) y-intercept 

(c) x-intercepts 

(d) Domain 

(e) Range 

(f) Line of symmetry 

(g) Is a positive or negative? 

(h) Is a -1 < a < 1 or a < -1 or a > 1? 




40 50 
length 

4. Use the stopping distance function from the lesson to find: 

(a) rf(45) 

(b) What speed has a stopping distance of about 96 feet? 

5. Using Galileo's law from the lesson, find: 

(a) The distance an object has fallen at 3.5 seconds 

(b) The total distance the object has fallen in 3.5 seconds 



Graph the following equations by making a table. Let -3 < x < 3. Determine the range of each equation. 



6. y = 2x 2 

7. y = -x 2 

8. y = x 2 -2x + 3 

9. y = 2jc 2 + 4x+1 
10. y = -x 2 + 3 



383 



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11. y = x 2 -8x + 3 

12. y = x 2 -A 



Which has a more positive y-intercept? 



+ 4 



13. 


y = 


x 2 or y = 


--Ax 2 




14. 


y = 


2x 2 + 4 or y = 


2 X 


15. 


y = 


-2x 2 -2 


or y - 


= -x 2 



Identify the vertex and y-intercept. Is the vertex a maximum or a minimum? 



16. y = x 2 -2x-8 

17. v = -jc 2 + 10jc-21 

18. y = 2x 2 + 6x + 4 



Does the graph of the parabola open up or down? 



19. y = -2x 2 - 2x - 3 

20. y = 3x 2 

21. y= 16-4jc 2 



Which equation has a larger vertex? 



22. y = jc 2 or y = 4jc 2 

23. y = -2x 2 or y = -2x 2 - 2 

24. y = 3jc 2 - 3 or y = 3x 2 - 6 



Graph the following functions by making a table of values. Use the vertex and x-intercepts to help you 
pick values for the table. 

25. y = 4x 2 -4 

26. y = -x 2 + x + 12 

27. y = 2jc 2 + 10x + 8 

28. y = \x 2 - 2x 

29. y = x - 2x 2 

30. y = 4jc 2 -8jc + 4 

31. Nadia is throwing a ball to Peter. Peter does not catch the ball and it hits the ground. The graph 
shows the path of the ball as it flies through the air. The equation that describes the path of the ball 
is y = 4 + 2x - 0.16x 2 . Here, y is the height of the ball and x is the horizontal distance from Nadia. 
Both distances are measured in feet. How far from Nadia does the ball hit the ground? At what 
distance, x, from Nadia, does the ball attain its maximum height? What is the maximum height? 

www.ckl2.org 384 



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4 6 8 10 12 14 
horizontal distance (feet) 

32. Peter wants to enclose a vegetable patch with 120 feet of fencing. He wants to put the vegetable 
patch against an existing wall, so he needs fence for only three of the sides. The equation for the 
area is given by a = 120x - x 2 . From the graph, find what dimensions of the rectangle would give 
him the greatest area. 













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20 30 40 

width (feet) 



Mixed Review 

33. Factor 6u 2 v - llu 2 v 2 - 10w 2 v 3 using its GCF. 

34. Factor into primes: 3x 2 + IIjc + 10. 

35. Simplify -±(63) (-f). 

36. Solve for b : \b + 2| = 9. 

37. Simplify (4x 3 y 2 z) 3 . 

38. What is the slope and y-intercept of 7x + 4y = 9? 

10.2 Solving Quadratic Equations by Graphing 

Isaac Newton's theory for projectile motion is represented by the equation: 

• t —time {usually in seconds) 

• 8 ^gravity due to acceleration; either 9.8m/ s 2 or 32ft/ s 2 



385 



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• vo = initial velocity 

• ho = initial height of object 

Consider the following situation: "A quarterback throws a football at an initial height of 5.5 feet with an 
initial velocity of 35 feet per second." 

By substituting the appropriate information: 

• g = 32 because the information is given in feet 

• vo = 35 

• ho = 5.5 

The equation becomes h(t) = -|(32)/ 2 + 35/ + 5.5 -> h(i) = -16t 2 + 35/ + 5.5. 
Using the concepts from the previous lesson, we know 

• The value of a is negative, so the parabola opens downward. 

• The vertex is a maximum point. 

• The y-intercept is (0, 5.5). 

• The graph is narrow about its line of symmetry. 

At what time will the football be 6 feet high? This equation can be solved by graphing the quadratic 
equation. 

Solving a Quadratic Using a Calculator 

Chapter 7 focused on how to solve systems by graphing. You can think of this situation as a system: 

( y = -16^ + 35^ + 5.5 

< . You are looking for the appropriate x-coordinates that give a y-coordinate of 6 

feet. Therefore, you are looking for the intersection of the two equations. 

Begin by typing the equations into the [Y =] menu of your calculator. Adjust the window until you see 
the vertex, y-intercept, x-intercepts, and the horizontal line of 6 units. 

Floti PlotE Plots 

\ViB-16X2+35X+5- 

5 

\Vh = 

WINDOW 
Xnin=0 
Xnax=3 
Xscl=l 
Vnin=0 
Vnax=30 
Vscl=2 
Xres=l 




www.ckl2.org 386 



By looking at the graph, you can see there are two points of intersection. Using the methods from chapter 
7, find both points of intersection. 

(0.014,6) and (2.172,6) 
At 0.014 seconds and again at 2.17 seconds, the football is six feet from the ground. 

Using a Calculator to Find the Vertex 

You can also use a graphing calculator to determine the vertex of the parabola. The vertex of this equation 
is a maximum point, so in the [CALCULATE] menu of the graphing option, look for [MAXIMUM]. 



lljyalue 

2=zero 

3:nininun 

4=naxiMun 

5= intersect 

6:dy^dx 

7=Xf<x)dx 



Choose option #4. The calculator will ask you, "LEFT BOUND?" Move the cursor to the left of the vertex 
and hit [ENTER]. 

The calculator will ask, "RIGHT BOUND?" Move the cursor to the right of the vertex and hit [ENTER]. 

Hit [ENTER] to guess. 

The maximum point on this parabola is (1.09, 24.64). 

Example 1: Will the football reach 25 feet high? 

Solution: The vertex represents the maximum point of this quadratic equation. Since its height is 24.64 
feet, we can safely say the football will not reach 25 feet. 

Example 2: When will the football hit the ground, assuming no one will catch it? 

( y = -16/ 2 + 35^ + 5.5 
Solution: We know want to know at what time the height is zero. < . By repeating 

[y = 

the process above and finding the intersection of the two lines, the solution is (2.33, 0). At 2.33 seconds, 

the ball will hit the ground. 

The point at which the ball reaches the ground (y = 0) represents the x-intercept of the graph. 

The x-intercept of a quadratic equation is also called a root, solution, or zero. 

Example: Determine the number of solutions to y = x 2 + 4. 

Solution: Graph this quadratic equation, either by hand or with a graphing calculator. Adjust the calcu- 
lator's window to see both halves of the parabola, the vertex, the x-axis, and the y-intercept. 

The solutions to a quadratic equation are also known as its x-intercepts. This parabola does not cross 
the x-axis. Therefore, this quadratic equation has no real solutions. 




i i i i i i i i 



387 www.ckl2.org 



Example: Andrew has 100 feet of fence to enclose a rectangular tomato patch. He wants to find the 
dimensions of the rectangle that encloses the most area. 

Solution: The perimeter of a rectangle is the sum of all four sides. Let w = width and / = length. The 
perimeter of the tomato patch is 100 = / + / + w + w — > 100 = 2/ + 2w. 

The area of a rectangle is found by the formula A = l(w) . We are looking for the intersection between the 
area and perimeter of the rectangular tomato patch. This is a system. 

Jl00 = 2/ + 2w 
[A = l{w) 

Before we can graph this system, we need to rewrite the first equation for either / or w. We will then use 
the Substitution Property. 

100 = 2/ + 2w -> 100 - 2/ = 2w 
100 - 2/ 



= w — > 50 - / = w 



2 

Use the Substitution Property to replace the variable w in the second equation with the express 50 - /. 

A = Z(50 - /) = 50/ - I 2 

Graph this equation to visualize it. 

WINDOW 
Xnin=0 
Xnax=60 
Xscl=5 
Vnin= "5 
Vnax=650 
Vscl=5Q 
Xres=l 




The parabola opens downward so the vertex is a maximum. The maximum value is (25, 625). The length 
of the tomato patch should be 25 feet long to achieve a maximum area of 625 square feet. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Quadratic Equations by Graphing (10:51) 

1. What are the alternate names for the solution to a parabola? 

2. Define the following variables in the function h(t) = -\{g)t 2 + v$t + ho. 

www.ckl2.org 388 




Figure 10.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/804 



(a) h 

(b) t 

(c) v 

(d) g 

(e) h{t) 



3. A rocket is launched from a height of 3 meters with an initial velocity of 15 meters per second. 

(a) Model the situation with a quadratic equation. 

(b) What is the maximum height of the rocket? When will this occur? 

(c) What is the height of the rocket after four seconds? What does this mean? 

(d) When will the rocket hit the ground? 

(e) At what time will the rocket be 13 meters from the ground? 



How many solutions does the quadratic equation have? 



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6. 


-x 2 + 3 = 


7. 


2x 2 + 5x - 7 


8. 


-x 2 + x - 3 : 



Find the zeros of the quadratic equations below. If necessary, round your answers to the nearest hundredth. 

9. y = -x 2 + 4x - 4 

10. y = 3x 2 - 5x 

11. x 2 + 3x + 6 = 

12. -2jc 2 + x + 4 = 

13. x 2 - 9 = 

14. x 2 + 6jc + 9 = 
IOjc 2 - 3x 2 = 



15. 
16. 



1^2 



2x + 3 = 



1 



17. y = -3jc 2 + 4x 

18. y = 9 - 4x 2 

19. y = x 2 + 7;c + 2 

20. y = -jt 2 -10;t-25 

21. y = 2jc 2 -3jc 

22. y = x 2 -2x + 5 

23. Andrew is an avid archer. He launches an arrow that takes a parabolic path, modeled by the equation 
y = -4.9t 2 + 48/. Find how long it takes the arrow to come back to the ground. 



For questions 24 - 26, 

(a) Find the roots of the quadratic polynomial. 

(b) Find the vertex of the quadratic polynomial. 



24. y = x 2 + 12* + 5 

25. y = jc 2 + 3jc + 6 

26. y = -x 2 -3x + 9 

27. Sharon needs to create a fence for her new puppy. She purchased 40 feet of fencing to enclose three 
sides of a fence. What dimensions will produce the greatest area for her puppy to play? 

28. An object is dropped from the top of a 100-foot-tall building. 

(a) Write an equation to model this situation. 



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390 



(b) What is the height of the object after 1 second? 

(c) What is the maximum height of the object? 

(d) At what time will the object be 50 feet from the ground? 

(e) When will the object hit the ground? 

Mixed Review 

29. Factor 3r 2 -4r+l. 

30. Simplify (2+ V3)(4+ V3). 

31. Write the equation in slope-intercept form and identify the slope and y-intercept: 9 - 3x + 18y = 0. 

32. The half life of a particular substance is 16 days. An organism has 100% of the substance on day 
zero. What is the percentage remaining after 44 days? 

33. Multiply and write your answer in scientific notation: 0.00000009865 x 123564.21 

34. A mixture of 12% chlorine is mixed with a second mixture containing 30% chlorine. How much of 
the 12% mixture is needed to mix with 80 mL to make a final solution of 150 mL with a 20% chlorine 
concentration? 

10.3 Solving Quadratic Equations Using Square 
Roots 

Suppose you needed to find the value of x such that x 2 = 81. How could you solve this equation? 

• Make a table of values. 

• Graph this equation as a system. 

• Cancel the square using its inverse operation. 

The inverse of a square is a square root. 

By applying the square root to each side of the equation, you get: 

x = ±V81 

x = 9 or x = -9 

In general, the solution to a quadratic equation of the form = ax 2 - c is: 

x = A /- or x = - -/- 
V a V a 

Example 1: Solve (x - 4) 2 - 9 = 0. 

Solution: Begin by adding 9 to each side of the equation. 

(x-4) 2 = 9 

Cancel square by applying square root. 

x-4 = 3orx-4: = -3 

Solve both equations for x : x = 7 or x = 1 

391 www.ckl2.org 



In the previous lesson, you learned Newton's formula for projectile motion. Let's examine a situation in 
which there is no initial velocity. When a ball is dropped, there is no outward force placed on its path; 
therefore, there is no initial velocity. 

A ball is dropped from a 40-foot building. When does the ball reach the ground? 

Using the equation from the previous lesson, h(t) = -\{g)t 2 + v$t + ho, and substituting the appropriate 
information, you get: 



Simplify 
Solve for x : 



= -I(32> 2 + (0)^ + 40 
= -16^+40 

-40 = -m 2 

2.5 = t 2 

t « 1.58 and t « -1.58 



Because t is in seconds, it does not make much sense for the answer to be negative. So the ball will reach 
the ground at approximately 1.58 seconds. 

Example: A rock is dropped from the top of a cliff and strikes the ground 1.2 seconds later. How high is 
the cliff in meters? 

Solution: Using Newton's formula, substitute the appropriate information. 



Simplify: 
Solve for ho : 



= --(9.8)(7.2) 2 + (0)(7.2) + /z 

= -254.016 + /z 
ho = 254.016 



The cliff is approximately 254 meters tall. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Quadratic Equations by Square Roots (11:03) 




Figure 10.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/805 



Solve each quadratic equation. 
www.ckl2.org 



392 



1. x 2 = 196 

2. x 2 - 1 = 

3. x 2 - 100 = 

4. x 2 + 16 = 

5. 9x 2 - 1 = 

6. 4x 2 -49 = 

7. 64x 2 -9 = 

8. x 2 - 81 = 

9. 25x 2 -36 = 

10. x 2 + 9 = 

11. x 2 -16 = 

12. x 2 -36 = 

13. 16x 2 -49 = 

14. (x-2) 2 = l 

15. (x + 5) 2 = 16 

16. (2x-l) 2 -4 = 

17. (3x + 4) 2 = 9 

18. (x-3) 2 + 25 = 

19. x 2_ 6 = 

20. x 2 -20 = 

21. 3x 2 + 14 = 

22. (x-6) 2 = 5 

23. (4x+l) 2 -8 = 

24. (x+10) 2 = 2 

25. 2(x + 3) 2 = 8 

26. How long does it take a ball to fall from a roof to the ground 25 feet below? 

27. Susan drops her camera in the river from a bridge that is 400 feet high. How long is it before she 
hears the splash? 

28. It takes a rock 5.3 seconds to splash in the water when it is dropped from the top of a cliff. How 
high is the cliff in meters? 

29. Nisha drops a rock from the roof of a building 50 feet high. Ashaan drops a quarter from the top- 
story window, which is 40 feet high, exactly half a second after Nisha drops the rock. Which hits the 
ground first? 

30. Victor drops an apple out of a window on the 10 ?/! floor, which is 120 feet above ground. One second 
later, Juan drops an orange out of a 6 t/! -floor window, which is 72 feet above the ground. Which fruit 
reaches the ground first? What is the time difference between the fruits' arrivai to the ground? 

Mixed Review 

31. Graph y — 2x 2 + 6x + 4. Identify the following: 

(a) Vertex 

(b) x-intercepts 

(c) y-intercepts 

(d) axis of symmetry 

32. What is the difference between y — x + 3 and y — x 2 + 3? 

33. Determine the domain and range of y = -(x — 2) 2 + 7. 

34. The Glee Club is selling hot dogs and sodas for a fundraiser. On Friday the club sold 112 hot dogs 
and 70 sodas and made $154.00. On Saturday the club sold 240 hot dogs and 120 sodas and made 
$300.00. How much is each soda? Each hot dog? 

393 www.ckl2.org 



10.4 Solving Quadratic Equations by Completing 
the Square 

There are several ways to write an equation for a parabola: 

• Standard form: y = ax 2 + bx + c 

• Factored form: y = {x + m)(x + n) 

• Vertex form: y = a(x - h) 2 + k 

Vertex form of a quadratic equation: y = a(x-h) 2 +k, where (h,k) = vertex of the parabola and a = leading 
coefficient 

Example 1: Determine the vertex of y = -\{x - 4) 2 - 7. Is this a minimum or a maximum point of the 
parabola? 

Solution: Using the definition of vertex form, h = 4, /: = -7. 

• The vertex is (4, -7). 

• Because a is negative, the parabola opens downward. 

• Therefore, the vertex (4, -7) is a maximum point of the parabola. 

Once you know the vertex, you can use symmetry to graph the parabola. 

Table 10.4: 

_^ y 

2 
3 

4 -7 

5 

6 

Example 2: Write the equation for a parabola with a = 3 and vertex (~4, 5) in vertex form. 
Solution: Using the definition of vertex form y = a(x - h) 2 + k, h = -4 and k = 5. 

y = 3(x-(-4)) 2 + 5 
y = 3(x + 4) 2 + 5 

Consider the quadratic equation y = x 2 + 4x - 2. What is its vertex? You could graph this using your 
calculator and determine the vertex or you could complete the square. 

Completing the Square 

Completing the square is a method used to create a perfect square trinomial, as you learned in the 
previous chapter. 

A perfect square trinomial has the form a 2 + 2 (ab) + /? 2 , which factors into (a + b) 2 . 

Example: Find the missing value to create a perfect square trinomial: x 2 + 8x+?. 

www.ckl2.org 394 



Solution: The value of a is x. To find /?, use the definition of the middle term of the perfect square trinomial. 

2 (ab) = 8x 

a is x, 2{xb) = 8x 

c i r i 2xb 8x i a 
bolve lor b : = > b = 4 

2x 2x 

To complete the square you need the value of b 2 . 

b 2 = 4 2 = 16 

The missing value is 16. 

To complete the square, the equation must be in the form: y = x 2 + ( \b\x + b 2 . 

Looking at the above example, ^(8) =4 and 4 2 = 16. 

Example 3: Find the missing value to complete the square of x 2 + 22x+?. Then factor. 

Solution: Use the definition of the middle term to complete the square. 

\{b) = 1(22) = 11 

Therefore, ll 2 = 121 and the perfect square trinomial is x 2 + 22x + 121. Rewriting in its factored form, 
the equation becomes (x + ll) 2 . 

Solve Using Completing the Square 

Once you have the equation written in vertex form, you can solve using the method learned in the last 
lesson. 

Example: Solve x 2 + 22* + 121 = 0. 

Solution: By completing the square and factoring, the equation becomes: 

(;t + ll) 2 = 
Solve by taking the square root: x + 11 = +0 

Separate into two equations: x -\- 11 = or x -\- 11 = 

Solve for x : x = -11 

Example: Solve x 2 + 10* + 9 = 0. 

Solution: Using the definition to complete the square, \{b) = ^(10) = 5. Therefore, the last value of the 
perfect square trinomial is 5 2 = 25. The equation given is 

x 2 + 10* + 9 = 0, and 9 * 25 
Therefore, to complete the square, we must rewrite the standard form of this equation into vertex form. 



Subtract 9: 



x 2 + 10* = -9 



Complete the square: Remember to use the Addition Property of Equality. 

395 www.ckl2.org 



Factor the left side. 
Solve using square roots. 



x 2 + lOx + 25 = -9 + 25 
(x + 5) 2 = 16 



V 



(;c + 5) 2 = ±Vl6 

x = -1 or x = -9 



Example: An arrow is shot straight up from a height of 2 meters with a velocity of 50 m/s. What is the 
maximum height that the arrow will reach and at what time will that happen? 

Solution: The maximum height is the vertex of the parabola. Therefore, we need to rewrite the equation 
in vertex form. 



We rewrite the equation in vertext form. 



Complete the square inside the parentheses. 



y = 

y-2 = 

y-2 = 

y-2-4.9(5.1) 2 = 
y - 129.45 = 



-4.9r + 50^ + 2 
-4.9/ 2 + 50/ 
-4.90 2 - 10.2f) 
-4.9(r 2 -10.2/+(5.1) 2 ) 
-4.9(/-5.1) 2 



The maximum height is 129.45 meters. 

Multimedia Link: Visit the http://www.mathsisfun.com/algebra/completing-square.html - math- 
isfun webpage for more explanation on completing the square. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Quadratic Equations by Completing the Square (14:06) 




Figure 10.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/806 



1. What does it mean to "complete the square"? 

2. Describe the process used to solve a quadratic equation by completing the square. 

3. Using the equation from the arrow in the lesson, 



www.ckl2.org 



396 



(a) How high will an arrow be four seconds after being shot? After eight seconds? 

(b) At what time will the arrow hit the ground again? 

Write the equation for the parabola with the given information. 

4. a = a, vertex = (h,k) 

5. a = |, vertex = (1, 1) 

6. a = -2, vertex = (-5,0) 

7. Containing (5, 2) and vertex (1, -2) 

8. a = 1, vertex = (-3,6) 

Complete the square for each expression. 

9. x 2 + 5x 

10. x 2 - 2x 

11. x 2 + 3x 

12. x 2 -4x 

13. 3jc 2 + 18jc 

14. 2x 2 -22x 

15. 8jc 2 - IOjc 

16. 5jc 2 + 12x 

Solve each quadratic equation by completing the square. 



17. 


x 2 - 4x — 5 


18. 


x 2 - 5x = 10 


19. 


x 2 + lOx + 15 = 


20. 


x 2 + 15x + 20 = 


21. 


2x 2 - 18x = 


22. 


4x 2 + 5x = -1 


23. 


10x 2 - 30x - 8 = 


24. 


5x 2 + 15x - 40 = 



Rewrite each quadratic function in vertex form. 



25. y = x 2 - 6x 

26. y + 1 = -2jc 2 - x 

27. y = 9x 2 + 3x - 10 

28. y = 32x 2 + 60jc+10 

For each parabola, find: 



1. The vertex 

2. x-intercepts 

3. y-intercept 

4. If it opens up or down 

5. The graph the parabola 



397 www.ckl2.org 



29. 


y - 4 = x 2 + 8x 


30. 


y = -4x 2 + 20x - 24 


31. 


j = 3x 2 + 15x 


32. 


j + 6 = -x 2 + x 


33. 


x 2 - IOjc + 25 = 9 



34. x 2 + 18jc + 81 = 1 

35. 4jc 2 -12jc + 9 = 16 

36. x 2 + 14jc + 49 = 3 

37. 4jc 2 - 20jk + 25 = 9 

38. x 2 + 8jc+16 = 25 

39. Sam throws an egg straight down from a height of 25 feet. The initial velocity of the egg is 16 ft/sec. 
How long does it take the egg to reach the ground? 

40. Amanda and Dolvin leave their house at the same time. Amanda walks south and Dolvin bikes east. 
Half an hour later they are 5.5 miles away from each other and Dolvin has covered three miles more 
than the distance that Amanda covered. How far did Amanda walk and how far did Dolvin bike? 

41. Two cars leave an intersection. One car travels north; the other travels east. When the car traveling 
north had gone 30 miles, the distance between the cars was 10 miles more than twice the distance 
traveled by the car heading east. Find the distance between the cars at that time. 



Mixed Review 



42. A ball dropped from a height of four feet bounces 70% of its previous height. Write the first five 
terms of this sequence. How high will the ball reach on its 8 th bounce? 

43. Rewrite in standard form: y = |x - 11. 

44. Graph y = 5(^J . Is this exponential growth or decay? What is the growth factor? 

45. Solve for r: |3r-4|<2. 

46. Solve for m : -2m + 6 = -8(5m + 4). 

47. Factor 4a 2 + 36a - 40. 



Quick Quiz 

1. Graph y = -3x 2 - Ylx - 13 and identify: 

(a) The vertex 

(b) The axis of symmetry 

(c) The domain and range 

(d) The y-intercept 

(e) The x-intercepts estimated to the nearest tenth 

2. Solve y = x 2 + 9x + 20 by graphing. 

3. Solve for x : 74 = x 2 - 7. 

4. A baseball is thrown from an initial height of 5 feet with an initial velocity of 100 ft/sec. 

(a) What is the maximum height of the ball? 

(b) When will the ball reach the ground? 

(c) When is the ball 90 feet in the air? 

5. Solve by completing the square: v 2 - 20v + 25 = 6 
www.ckl2.org 398 



10.5 Solving Quadratic Equations Using the Quadratic 
Formula 

This chapter has presented three methods to solve a quadratic equation: 



By graphing to find the zeros; 

By solving using square roots; and 

By using completing the square to find the solutions 



This lesson will present a fourth way to solve a quadratic equation: using the Quadratic Formula. 



History of the Quadratic Formula 

As early as 1200 BC, people were interested in solving quadratic equations. The Babylonians solved 
simultaneous equations involving quadratics. In 628 AD, Brahmagupta, an Indian mathematician, gave 
the first explicit formula to solve a quadratic equation. The Quadratic Formula was written as it is today 
by the Arabic mathematician Al-Khwarizmi. It is his name upon which the word "Algebra" is based. 

The solution to any quadratic equation in standard form = ax 2 + bx + c is 

-b± V/? 2 - 4ac 

x = ^ 

2a 

Example: Solve x 2 + lOx + 9 = using the Quadratic Formula. 

Solution: We know from the last lesson the answers are x = -1 or x = -9. 

By applying the Quadratic Formula and a = l,b = 10, and c = 9, we get: 





-10 ± V(10) 2 -4(l)(9) 


X — 


2(1) 




-10 ± V100 - 36 


X — 


2 




-10 ± a/64 


X — 






2 




-10 ±8 


X — 






2 




-10 + 8 -10-8 


X = 


or x = 




2 2 


X — 


-1 or x — -9 



Example 1: Solve -4x 2 + x + 1 = using the Quadratic Formula. 
Solution: 



399 www.ckl2.org 



Quadratic formula: 

Plug in the values a = -4, b = 1, c = 1. 

Simplify. 

Separate the two options. 
Solve. 





-fe ± VZ? 2 - 4ac 


X — 


2a 




-l±V(l) 2 -4(-4)(l) 


X — 


2(-4) 


X = 


-1+ VI + 16 -1+ V17 

-8 ~ -8 


X = 


-1+ Vl7 , -1- Vl7 
and x = 

-8 -8 


X « 


-.39 and x « .64 



Multimedia Link For more examples of solving quadratic equations using the Quadratic Formula, see 
Khan Academy Equation Part 2 (9:14). 




Figure 10.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/94 

Figure 2 provides more examples of solving equations using the quadratic equation. This video is not nec- 
essarily different from the examples above, but it does help reinforce the procedure of using the Quadratic 
Formula to solve equations. 

Finding the Vertex of a Quadratic Equation in Standard Form 

The x-coordinate of the vertex of = ax 2 + bx + c is x = -| 

Which Method to Use? 

Usually you will not be told which method to use. You will have to make that decision yourself. However, 
here are some guidelines to which methods are better in different situations. 

• Graphing - a good method to visualize the parabola and easily see the intersections. Not always 
precise. 

• Factoring - best if the quadratic expression is easily factorable 

• Taking the square root - is best used of the form = ax 2 - c 

• Completing the square - can be used to solve any quadratic equation. It is a very important 
method for rewriting a quadratic function in vertex form. 

• Quadratic Formula - is the method that is used most often for solving a quadratic equation. If 
you are using factoring or the Quadratic Formula, make sure that the equation is in standard form. 



www.ckl2.org 



400 



Example: The length of a rectangular pool is 10 meters more than its width. The area of the pool is 875 
square meters. Find the dimensions of the pool. 

Solution: Begin by drawing a sketch. The formula for the area of a rectangle is A = l(w). 




x+10 

A = (jc+10)(jc) 
875 = x 2 + IOjc 

Now solve for x using any method you prefer. 

The result is x = 25. So, the length of the pool is 35 meters and the width is 25 meters. 

Practice Set 

The following video will guide you through a proof of the Quadratic Formula. CK-12 Basic Algebra: Proof 
of Quadratic Formula (7:44) 




Figure 10.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/807 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Using the Quadratic Formula (16:32) 




Figure 10.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/808 



1. What is the Quadratic Formula? When is the most appropriate situation to use this formula? 

401 www.ckl2.or£ 



2. When was the first known solution of a quadratic equation recorded? 
Find the x-coordinate of the vertex of the following equations. 

3. x 2 - 14* + 45 = 

4. 8x 2 -16x-42 = 

5. 4x 2 + 16x+12 = 

6. x 2 + 2x-15 = 

Solve the following quadratic equations using the Quadratic Formula. 



7. 


x 2 + 4x - 21 = 


8. 


x 2 - 6x = 12 


9. 


OJi ~CJ Ji ~0 


10. 


2x 2 + x - 3 = 


11. 


-x 2 - 7x + 12 = 


12. 


-3x 2 + 5x = 


13. 


4x 2 = 


14. 


x 2 + 2x + 6 = 



Solve the following quadratic equations using the method of your choice. 

15. x 2 -x = 6 

16. x 2 - 12 = 

17. -2jc 2 + 5x-3 = 

18. x 2 + 7jk-18 = 

19. 3jc 2 + 6x = -10 

20. -4x 2 + 4000x = 

21. -3jc 2 + 12x+1 = 

22. x 2 + 6x + 9 = 

23. 81x 2 + 1 = 

24. -4jc 2 + 4x = 9 

25. 36jc 2 -21 = 

26. x 2 + 2x-3 = 

27. The product of two consecutive integers is 72. Find the two numbers. 

28. The product of two consecutive odd integers is 11 less than 3 times their sum. Find the integers. 

29. The length of a rectangle exceeds its width by 3 inches. The area of the rectangle is 70 square inches. 
Find its dimensions. 

30. Suzie wants to build a garden that has three separate rectangular sections. She wants to fence around 
the whole garden and between each section as shown. The plot is twice as long as it is wide and the 
total area is 200 square feet. How much fencing does Suzie need? 



2x 



piece of wood is 4 feet x 8 feet and the cut off part is \ of the total area of the plywood sheet. What 



31. Angel wants to cut off a square piece from the corner of a rectangular piece of plywood. The larger 
piece of wood is 4 feet x 8 feet and the 
is the length of the side of the square? 

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32. Mike wants to fence three sides of a rectangular patio that is adjacent the back of his house. The 
area of the patio is 192 ft 2 and the length is 4 feet longer than the width. Find how much fencing 
Mike will need. 

33. 




Mixed Review 



33. The theatre has three types of seating: balcony, box, and floor. There are four times as many floor 
seats as balcony. There are 200 more box seats than balcony seats. The theatre has a total of 1,100 
seats. Determine the number of balcony, box, and floor seats in the theatre. 

34. Write an equation in slope-intercept form containing (10, 65) and (5, 30). 

35. 120% of what number is 60? 

36. Name the set() of numbers to which Vl6 belongs. 



37. Divide 6± 



-2^ 



38. The set is the number of books in a library. Which of the following is the most appropriate domain 
for this set: all real numbers; positive real numbers; integers; or whole numbers? Explain your 
reasoning. 



10.6 The Discriminant 



You have seen parabolas that intersect the x-axis twice, once, or not at all. There is a relationship between 
the number of real x-intercepts and the Quadratic Formula. 

Case 1: The parabola has two x-intercepts. This situation has two possible solutions for jc, because the 



value inside the square root is positive. Using the Quadratic Formula, the solutions are x = 



and x 



-b-^b 2 -4ac 
2a 



-b+^b 2 -4ac 
2a 



















H 


n 


i 
















































/ 












































































<-i 






L 






























































u 








































































r 






































n 






















































x 














j 
















10 


-8 "-6 '-4 \-2 ' - 


. £ 4 
















































\ A 






























































































































































a 


















































































-1 


(V 

























Case 2: The parabola has one x-intercept. This situation occurs when the vertex of the parabola just 
touches the x-axis. This is called a repeated root, or double root. The value inside the square root is 
zero. Using the Quadratic Formula, the solution is x 



2a' 



403 



www.ckl2.org 











A. 


k 




















J 








/ 












\ 


ft 








/ 












\ 










/ 












\ 


A 








/ 














\= 






/ 
















X 






/ 






















/ 


















v/ 








X 


J -H 


i -: 


5 -5 


1 .' 






: 


; : 


i - 


> J 












■1 ■ 















Case 3; The parabola has no x-intercept. This situation occurs when the parabola does not cross the 
x-axis. The value inside the square root is negative, therefore there are no real roots. The solutions to 
this type of situation are imaginary, which you will learn more about in a later textbook. 











*i 


\ 
















\ 




ru* 






1 












\ 








\ 


1 














\ 






















\ 


6- 




















\ 


L F>- 


- 


1 


















K 


J 




















1* 






















a* 






















'£," 


































X 



-5-4-3-2-1 12 3 4 5 

The value inside the square root of the Quadratic Formula is called the discriminant. It is symbolized 
by D. It dictates the number of real solutions the quadratic equation has. This can be summarized with 
the Discriminant Theorem. 

• If D > 0, the parabola will have two x-intercepts. The quadratic equation will have two real solutions. 

• If D = 0, the parabola will have one x-intercept. The quadratic equation will have one real solution. 

• If D < 0, the parabola will have no x-intercepts. The quadratic equation will have zero real solutions. 

Example 1: Determine the number of real solutions to -3x 2 + 4x + 1 = 0. 

Solution: By finding the value of its discriminant, you can determine the number of x-intercepts the 
parabola has and thus the number of real solutions. 

D = b 2 -4(a)(c) 

D=(4) 2 -4(-3)(l) 
D = 16 + 12 = 28 

Because the discriminant is positive, the parabola has two real x-intercepts and thus two real solutions. 
www.ckl2.org 404 



Example: Determine the number of solutions to -2x 2 + x = 4. 

Solution: Before we can find its discriminant, we must write the equation in standard form ax 2 -\-bx-\-c = 0. 

Subtract 4 from each side of the equation: -2x 2 + x - 4 = 0. 



Find the discriminant. 



D = (l)'-4(-2)(-4) 
D= 1-32 = -31 



The value of the discriminant is negative; there are no real solutions to this quadratic equation. The 
parabola does not cross the x-axis. 

Example 2: Emma and Bradon own a factory that produces bike helmets. Their accountant says that 
their profit per year is given by the function P = 0.003x 2 + 12x + 27, 760, where x represents the number of 
helmets produced. Their goal is to make a profit of $40,000 this year. Is this possible? 

Solution: The equation we are using is 40, 000 = 0.003x 2 + 12x + 27, 760. By finding the value of its 
discriminant, you can determine if the profit is possible. 

Begin by writing this equation in standard form: 

= 0.003jc 2 + 12jc-12,240 
D = b 2 -4(a)(c) 
D= (12) 2 -4(0.003)(-12,240) 
D = 144 + 146.88 = 290.88 

Because the discriminant is positive, the parabola has two real solutions. Yes, the profit of $40,000 is 
possible. 

Multimedia Link: This http : //sciencestage . com/v/20592/a-level-maths- : -roots-of - a- quadrat i c-equ at i< 
-discriminant- :-examsolutions .html - video, presented by Science Stage, helps further explain the dis- 
criminant using the Quadratic Formula. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Discriminant of Quadratic Equations (10:14) 




Figure 10.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/809 



405 



www.ckl2.org 



1. What is a discriminant? What does it do? 

2. What is the formula for the discriminant? 

3. Can you find the discriminant of a linear equation? Explain your reasoning. 

4. Suppose D = 0. Draw a sketch of this graph and determine the number of real solutions. 

5. D = -2.85. Draw a possible sketch of this parabola. What is the number of real solutions to this 
quadratic equation. 

6. D > 0. Draw a sketch of this parabola and determine the number of real solutions. 

Find the discriminant of each quadratic equation. 

7. 2x 2 - 4x + 5 = 

8. x 2 - 5x = 8 

9. 4jc 2 -12jc + 9 = 

10. jc 2 + 3jc + 2 = 

11. x 2 -16x = 32 

12. -5jc 2 + 5x-6 = 

Determine the nature of the solutions of each quadratic equation. 



13. 


-x 2 + 3x - 6 = 


14. 


5x 2 = 6x 


15. 


41x 2 - 31jc - 52 = 


16. 


x 2 - 8x + 16 = 


17. 


-x 2 + 3x - 10 = 


18. 


x 2 - 64 = 



A solution to a quadratic equation will be irrational if the discriminant is not a perfect square. If 
the discriminant is a perfect square, then the solutions will be rational numbers. Using the discriminant, 
determine whether the solutions will be rational or irrational. 

19. x 2 = -4x + 20 

20. x 2 + 2x - 3 = 

21. 3x 2 -llx= 10 

22. ^jc 2 + 2x+ | =0 

23. x 2 -10x + 25 = 

24. x 2 = 5x 

25. Marty is outside his apartment building. He needs to give Yolanda her cell phone but he does not 
have time to run upstairs to the third floor to give it to her. He throws it straight up with a vertical 
velocity of 55 feet/second. Will the phone reach her if she is 36 feet up? (Hint: The equation for the 
height is given by y = -32t 2 + 55/ + 4.) 

26. Bryson owns a business that manufactures and sells tires. The revenue from selling the tires in the 
month of July is given by the function R = x(200 - OAx) where x is the number of tires sold. Can 
Bryson's business generate revenue of $20,000 in the month of July? 

27. Marcus kicks a football in order to score a field goal. The height of the ball is given by the equation 
y = -gf^o* 2 ~^~ •*' wnere y i s t ne height and x is the horizontal distance the ball travels. We want to 
know if Marcus kicked the ball hard enough to go over the goal post, which is 10 feet high. 

Mixed Review 

www.ckl2.org 406 



28. Factor 6x 2 -jc-12. 

29. Find the vertex of y = -|x 2 - 3x - 12 = v by completing the square. 

30. Solve using the Quadratic Formula: -Ax 2 - 15 = -Ax. 

31. How many centimeters are in four fathoms? (Hint: 1 fathom = 6 feet) 

f 3* + 2y < -4 

[x-y>-3 
33. How many ways can 3 toppings be chosen from 7 options? 



32. Graph the solution to 



10.7 Linear, Exponential, and Quadratic Models 

So far in this text you have learned how to graph three very important types of equations. 

• Linear equations in slope-intercept form y = mx + b 

• Exponential equations of the form y = a(b) x 

• Quadratic equations in standard form y = ax 2 + bx + c 

In real-world applications, the function that describes some physical situation is not given. Finding the 
function is an important part of solving problems. For example, scientific data such as observations of 
planetary motion are often collected as a set of measurements given in a table. One job for the scientist is 
to figure out which function best fits the data. In this lesson, you will learn some methods that are used 
to identify which function describes the relationship between the dependent and independent variables in 
a problem. 

Using Differences to Determine the Model 

By finding the differences between the dependent values, we can determine the degree of the model for 
the data. 

• If the first difference is the same value, the model will be linear. 

• If the second difference is the same value, the model will be quadratic. 

• If the number of times the difference has been taken exceeds five, the model may be exponential or 
some other special equation. 



X 


y 


-2 


-4 


-1 


-1 





2 


1 


5 


2 


8 



difference of 
y- values 



-1+4 =3 
2+1 =3 
} 5-2 =3 
} 8-5 =3 



Example: The first difference is the same value (3). This data can be modeled using a linear regression 
line. 



407 



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The equation to represent this data is y = 3x + 2 

When we look at the difference of the y— values, we must make sure that we examine entries for which the 
x- values increase by the same amount. 

For example, examine the values in the following table. 

At first glance, this function might not look linear because the difference in the y— values is not always the 



same. 



difference of 
x- values 

1-0= 1 { 
3-1 -2 { 

4-3 = l{ 
6-4 = 2-[ 



X 


y 





5 


1 


10 


3 


20 


4 


25 


6 


35 



difference of 
y— values 

] -1+4=3 
} 2 +1 =3 
} 5-2 =3 
} 8-5 =3 



However, we see that the difference in y-values is 5 when we increase the x- values by 1, and it is 10 when 
we increase the x— values by 2. This means that the difference in y-values is always 5 when we increase 
the x-values by 1. Therefore, the function is linear. 

The equation is modeled by y = 5x + 5. 

An example of a quadratic model would have the following look when taking the second difference. 



X 


y-lx 2 3x + 1 


difference of difference of 
y- values differences 








; -i =-i, 

j L3+1 = 4 

* 3- =3 J 

" [ 1 -3 = 4 

MO- 3 = 7 y 


1 


1 


2 


3 


3 


10 


\ 11-7 = 4 
| 21 - 10 = 11 J 

> 15-11= 4 
} 36 -21 =15> 

kl9 -15= 4 
J55 -36 = 19 J 


4 


21 


5 


36 


6 


55 



Using Ratios to Determine the Model 

Finding the difference involves subtracting the dependent values leading to a degree of the model. By- 
taking the ratio of the values, one can obtain whether the model is exponential. 

If the ratio of dependent values is the same, then the data is modeled by an exponential equation, as in 
the example below. 



www.ckl2.org 



408 



X 


y 





4 


1 


12 


2 


36 


3 


108 


4 


324 



ratio of 
y - values 



\ 11 = 

J 4 

1 36 _ 

J 12 

1 108 

) 36 

I 324 

J 108 



3 

3 

3 

= 3 



Determine the Model Using a Graphing Calculator 

To enter data into your graphing calculator, find the [STAT] button. Choose [EDIT]. 

I.CRLC TESTS 

^"SortFK 
3:SortD< 
4:Clrl_ist 
5:SetU>Edit.or 




L1 



L£ 



L3 



L1(1) = 



[LI] represents your independent variable, your x. 
[L2] represents your dependent variable, your y. 



Enter the data into the appropriate list. Using the first set of data to illustrate yields: 



L1 


12 


L3 


2 


■E 


■H 






■i 


-i 









2 






1 


s 






2 


Immm 







L^lhJ = 



You already know this data is best modeled by a linear regression line. Using the [CALCULATE] menu 
of your calculator, find the linear regression line, linreg. 



409 



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EDIT 



TESTS 



mi-JIrTtats 

7i 2-Uar Stats 

3:Med-Med 

4:LinRe9<ax+b> 

5:QuadRe9 

6:CubicRe9 

7-i-QuartReg 

LinReg 
y=ax+b 
a=2.6 
b=1.6 

Look at the screen above. This is where you can find the quadratic regression line [QUADREG], the 
cubic regression line [CUBICREG], and the exponential regression line, [EXPREG]. 

Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Linear, Quadratic, and Exponential Models (8:15) 




Figure 10.10: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/811 



1. The second set of differences have the same value. What can be concluded? 

2. Suppose you find the difference five different times and still don't come to a common value. What 
can you safely assume? 

3. Why would you test the ratio of differences? 

4. If you had a cubic (3 rrf -degree) function, what could you conclude about the differences? 

Determine whether the data can be modeled by a linear equation, a quadratic equation, or neither. 
5. 



6. 



x 

y 



X 

y 



10 



-2 



-1 





2 



1 
3 




-2 

2 
6 



-5 

3 
11 



x 

y 



o 

50 



1 

75 



2 
100 



3 
125 



4 
150 



5 
175 



www.ckl2.org 



410 



9. 



10. 



X 


-10 


-5 







5 




10 




15 


y 


10 


2.5 







2.5 




10 




22.5 


X 


1 


2 


3 




4 




5 




6 


y 


4 


6 


6 




4 









-6 


X 


-3 


-2 




-1 









1 


2 


y 


-27 


-8 




-1 









1 


8 



Can the following data be modeled with an exponential function? 
11. 



12. 



13. 



X 





1 


2 


3 


4 


5 


y 


200 


300 


1800 


8300 


25, 800 


62, 700 


X 





1 


2 


3 


4 


5 


y 


120 


180 


270 


405 


607.5 


911.25 


X 





1 


2 


3 


4 


5 


y 


4000 


2400 


1440 


864 


518.4 


311.04 



Determine whether the data is best represented by a quadratic, linear, or exponential function. Find the 
function that best models the data. 

14. 



15. 



16. 



X 









1 




2 






3 


4 


y 


400 






500 




625 






781.25 


976.5625 


X 


-9 






-7 




-5 






-3 


-1 1 


y 


-3 






-2 




-1 









1 2 


X 


-3 


— 


2 




-1 









1 


2 3 


y 


14 


4 






-2 






4 


-2 


4 14 



17. As a ball bounces up and down, the maximum height it reaches continually decreases. The table 
below shows the height of the bounce with regard to time. 

(a) Using a graphing calculator, create a scatter plot of this data. 

(b) Find the quadratic function of best fit. 

(c) Draw the quadratic function of best fit on top of the scatter plot. 

(d) Find the maximum height the ball reaches. 

(e) Predict how high the ball is at 2.5 seconds. 



411 www.ckl2.org 



Table 10.5: 



Time (seconds) Height (inches) 

2 2 

2.2 16 

2.4 24 

2.6 33 

2.8 38 

3.0 42 

3.2 36 

3.4 30 

3.6 28 

3.8 14 

4.0 6 



18. A chemist has a 250-gram sample of a radioactive material. She records the amount remaining in 
the sample every day for a week and obtains the following data. 

(a) Draw a scatter plot of the data. 

(b) Which function best suits the data: exponential, linear, or quadratic? 

(c) Find the function of best fit and draw it through the scatter plot. 

(d) Predict the amount of material present after 10 days. 

Table 10.6: 

Day Weight (grams) 

250 

1 208 

2 158 

3 130 

4 102 

5 80 

6 65 

7 50 



19. The following table show the pregnancy rate (per 1000) for U.S. women aged 15 - 19 (source: US 
Census Bureau). Make a scatter plot with the rate as the dependent variable and the number of 
years since 1990 as the independent variable. Find which model fits the data best. Use this model 
to predict the rate of teen pregnancy in the year 2010. 

Table 10.7: 

Year Rate of Pregnancy (per 1000) 

1990 116.9 

1991 115.3 

1992 111.0 

1993 108.0 



www.ckl2.org 412 



Table 10.7: (continued) 



Year Rate of Pregnancy (per 1000) 

1994 104.6 

1995 99.6 

1996 95.6 

1997 91.4 

1998 88.7 

1999 85.7 

2000 83.6 

2001 79.5 

2002 75.4 

Mixed Review 

20. Cam bought a bag containing 16 cups of flour. He needs 2^ cups for each loaf of bread. Write this 
as an equation in slope-intercept form. When will Cam run out of flour? 

21. A basketball is shot from an initial height of 7 feet with an velocity of 10 ft/sec. 

(a) Write an equation to model this situation. 

(b) What is the maximum height the ball reaches? 

(c) What is the y-intercept? What does it mean? 

(d) When will the ball hit the ground? 

(e) Using the discriminant, determine whether the ball will reach 11 feet. If so, how many times? 

22. Graph y = \x - 2| + 3. Identify the domain and range of the graph. 

23. Solve 6>-5(c + 4) + 10. 

24. Is this relation a function? {(-6, 5), (-5, -3), (-2, -1), (0, -3), (2, 5)}. If so, identify its domain and 
range. 

25. Name and describe five problem-solving strategies you have learned so far in this chapter. 

10.8 Problem- Solving Strategies: Choose a Func- 
tion Model 

As you learn more and more mathematical methods and skills, it is important to think about the purpose 
of mathematics and how it works as part of a bigger picture. Mathematics is used to solve problems that 
often arise from real-life situations. Mathematical modeling is a process by which we start with a 
real-life situation and arrive at a quantitative solution. 

Modeling involves creating a set of mathematical equations that describes a situation, solving those equa- 
tions, and using them to understand the real-life problem. 

Often the model needs to be adjusted because it does not describe the situation as well as we wish. 

A mathematical model can be used to gain understanding of a real-life situation by learning how the system 
works, which variables are important in the system, and how they are related to each other. Models can 
also be used to predict and forecast what a system will do in the future or for different values of a parameter. 
Lastly, a model can be used to estimate quantities that are difficult to evaluate exactly. 

Mathematical models are like other types of models. The goal is not to produce an exact copy of the "real" 
object but rather to give a representation of some aspect of the real thing. The modeling process can be 
summarized as a flow chart: 

413 www.ckl2.org 



Real life 
problemf 



Describe 
assumption 




Change 
assumptions 



No 



Describe t he 
problem in 
mathematical terms! 



Solve the 
problem 




*\ 



Does the solution 
capture the real - 
life situation? 



W 



<; 



Interpret the 
solution in the 
real life situation 



Model is 
suitable 



Notice that the modeling process is very similar to the problem-solving format we have been using through- 
out this book. One of the most difficult parts of the modeling process is determining which function best 
describes a situation. We often find that the function we choose is not appropriate. Then we must choose 
a different one. 

Consider an experiment regarding the elasticity of a spring. 

Example: A spring is stretched as you attach more weight at its bottom. The following table shows the 
length of the spring in inches for different weights in ounces. 



ight (oz) 





2 


4 


6 


lgth (in) 


2 


2.4 


2.8 


3.2 



3.5 



10 
3.9 



12 
4.1 



14 

4.4 



16 
4.6 



18 
4.7 



20 
4.8 



a) Find the length of the spring as a function of the weight attached to it. 

b) Find the length of the spring when you attach 5 ounces. 

c) Find the length of the spring when you attach 19 ounces. 

Solution: Begin by graphing the data to get a visual of what the model may look like. 



5) 

5 



^ 




























































4 6 
















c 
















' 
























. 3 




by 


























































2 4 6 & 10 12 14 15 18 20 

weight (ounces) 



This data clearly does not fit a linear equation. It has a distinct curve that will not be modeled well 

by a straight line. 

Nor does this graph seem to fit a parabolic shape; thus it is not modeled by a quadratic equation. 



www.ckl2.org 



414 



• The curve does not fit the exponential curves studied in Chapter 8. 

• By taking the third set of differences, the value is approximately equal. Use the methods learned in 
the previous lesson to find a cubic regression equation. Check by graphing to see if this model is a 
good fit. 

Example: A golf ball is hit down a straight fairway. The following table shows the height of the ball with 
respect to time. The ball is hit at an angle of 70° with the horizontal with a speed of 40 meters/sec. 

Time (sec) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 

Height (meters) 17.2 31.5 42.9 51.6 57.7 61.2 62.3 61.0 57.2 51.0 42.6 31.9 19.0 4.1 

a) Find the height of the ball as a function of time. 

b) Find the height of the ball when t = 2.4 seconds. 

c) Find the height of the ball when t = 6.2 seconds. 




Solution: Begin by graphing the data to visualize the model. 

This data fits a parabolic curve quite well. We can therefore conclude the best model for this data is a 
quadratic equation. 

To solve part a), use the graphing calculator to determine the quadratic regression line. 

y = -4.92x 2 + 34.7x+1.2 

b) The height of the ball when t = 2.4 seconds is: 

y = -4.92(2.4) 2 + 34.7(2.4) + 1.2 = 56.1 meters 

c) The height of the ball when t = 6.2 seconds is 



y = -4.92(6.2) 2 + 34.7(6.2) + 1.2 = 27.2 meters 

415 



www.cki2.0rg 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Identifying Quadratic Models (8:05) 




Figure 10.11: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/812 

CK-12 Basic Algebra: Identifying Exponential Models (4:00) 




Figure 10.12: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/813 



CK-12 Basic Algebra: Quadratic Regression (9:17) 




Figure 10.13: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/814 



1. A thin cylinder is filled with water to a height of 50 centimeters. The cylinder has a hole at the 

bottom that is covered with a stopper. The stopper is released at time t = seconds and allowed to 

empty. The following data shows the height of the water in the cylinder at different times. 

Time (sec) 2 4 6 8 10 12 14 16 18 20 22 24 

Height (cm) 50 42.5 35.7 29.5 23.8 18.8 14.3 10.5 7.2 4.6 2.5 1.1 0.2 



www.ckl2.org 



416 



4 


8 


12 


16 


20 


24 


28 


15 


75 


343 


1139 


1864 


1990 


1999 



(a) What seems to be the best model for this situation? 

(b) Find the linear regression line and determine the height of the water at 4.2 seconds. 

(c) Find a quadratic equation and determine the height of the water at 4.2 seconds. 

(d) Find a cubic regression line and determine the height of the water at 4.2 seconds. 

(e) Which of these seems to be the best fit? 

(f) Using the function of best fit, find the height of the water when t = 5 seconds. 

(g) Using the function of best fit, find the height of the water when t = 13 seconds. 

2. A scientist counts 2,000 fish in a lake. The fish population increases at a rate of 1.5 fish per generation 

but the lake has space and food for only 2,000,000 fish. The following table gives the number of fish 

(in thousands) in each generation. 
Generation 

Number (thousands) 2 

(a) Which function seems to best fit the dataL linear, quadratic, or exponential? 

(b) Find the model for the function of best fit. 

(c) Find the number of fish as a function of generation. 

(d) Find the number of fish in generation 10. 

(e) Find the number of fish in generation 25. 

3. Using the golf ball example, find the maximum height the ball reaches. 

4. Using the golf ball example, evaluate the height of the ball at 5.2 seconds. 

Mixed Review 

5. Evaluate 2 -f 6 • 5 + 3 2 - 11 • 9*. 

6. 60 shirts cost $812.00 to screen print. 115 shirts cost $1,126.00 to screen print. Assuming the 
relationship between the number of shirts and the total cost is linear, write an equation in point- 
slope form. 

(a) What is the start-up cost (the cost to set up the screen)? 

(b) What is the slope? What does it represent? 

7. Solve by graphing: y = x 2 + 3x - 1. 

8. Simplify f. 

2 

9. Newton's Second Law states F = m- a. Rewrite this equation to solve for m. Use it to determine the 
mass if the force is 300 Newtons and the acceleration is 70m/ s 2 . 

10. The area of a square game board is 256 square inches. What is the length of one side? 

3 
1000' 



11. Write as a percent: -^ 



10.9 Chapter 10 Review 

Define each term. 

1. Vertex 

2. Standard form for a quadratic equation 

3. Model 

4. Discriminant 

Graph each function. List the vertex (round to the nearest tenth, if possible) and the range of the function. 

417 www.ckl2.org 



5. y = x 2 - 6x + 11 

6. y = -4x 2 + 16x - 19 

7. j = -x 2 - 2x + 1 

8. j = \x 2 + 8x + 6 

9. y = x 2 + 4x 

10. ) , = -I x 2 + 8x _4 

11. j=(x + 4) 2 + 3 

12. y = -(x-3) 2 -6 

13. y = (x-2) 2 + 2 

14. ) , = -( x + 5)2_i 

Rewrite in standard form. 

15. x-24 = -5x 

16. 5 + 4a = a 2 

17. -6 - 18a 2 = -528 

18. y = -( x + 4) 2 + 2 

Solve each equation by graphing. 

19. x 2 -8x + 87 = 9 

20. 23x + x 2 -104 = 4 

21. 13 + 26x = -x 2 + llx 

22. x 2 - 9x = 119 

23. -32 + 6x 2 -4x = 

Solve each equation by taking its square roots. 

24. x 2 = 225 

25. x 2 - 2 = 79 

26. x 2 + 100 = 200 

27. 8x 2 -2 = 262 

28. -6 - 4x 2 = -65 

29. 703 = 7x 2 + 3 

30. 10 + 6x 2 = 184 

31. 2 + 6x 2 = 152 

Solve each equation by completing the square then taking its square roots. 

32. n 2 - An - 3 = 9 

33. h 2 + 10/2 + 1 = 3 

34. x 2 + 14* - 22 = 10 

35. t 2 - 10? = -9 

Determine the maximum/minimum point by completing the square. 

36. x 2 - 20x + 28 = -8 

37. a 2 + 2 - 63 = -5 

www.ckl2.org 418 



38. x 2 + 6x-33 = 4 

Solve each equation by using the Quadratic Formula. 

39. 4x 2 - 3x = 45 

40. -5jc+11x 2 = 15 

41. -3r= 12r 2 -3 

42. 2m 2 + 10m = 8 

43. 7c 2 + 14c - 28 = -7 

44. 3w 2 - 15 = -3w 

In 45-50, for each quadratic equation, determine: 

(a) the discriminant 

(b) the number of real solutions 

(c) whether the real solutions are rational or irrational 

45. 4x 2 -4x+l = 

46. 2x 2 -x-3 = 

47. -2jc 2 - x - 1 = -2 

48. 4x 2 -8x + 4 = 

49. -5jc 2 + 10x-5 = 

50. 4jc 2 + 3x + 6 = 

51. Explain the difference between y = x 2 + 4 and y = -x 2 + 4. 

52. Jorian wants to enclose his garden with fencing on all four sides. He has 225 feet of fencing. What 
dimensions would give him the largest area? 

53. A ball is dropped off a cliff 70 meters high. 

(a) Using Newton's equation, model this situation. 

(b) What is the leading coefficient? What does this value tell you about the shape of the parabola? 

(c) What is the maximum height of the ball? 

(d) Where is the ball after 0.65 seconds? 

(e) When will the ball reach the ground? 

54. The following table shows the number of hours spent per person playing video games for various 

years in the United States. 

y x 1995 1996 1997 1998 1999 2000 

y 24 25 37 43 61 70 

(a) What seems to be the best function for this data? 

(b) Find the best fit function. 

(c) Using your equation, predict the number of hours someone will spend playing video games in 
2012. 

(d) Does this value seem possible? Explain your thoughts. 

55. The table shows the amount of money spent (in billions of dollars) in the U.S. on books for various 
years. 



X 


1990 


1991 


1992 


1993 


1994 


1995 


1996 


1997 


1998 


y 


16.5 


16.9 


17.7 


18.8 


20.8 


23.1 


24.9 


26.3 


28.2 



(a) Find a linear model for this data. Use it to predict the dollar amount spent in 2008. 

(b) Find a quadratic model for this data. Use it to predict the dollar amount spent in 2008. 

419 www.ckl2.org 



(c) Which model seems more accurate? Use the best model to predict the dollar amount spent in 
2012. 

(d) What could happen to change this value? 

56. The da^ta belof^ows th^^mber #$>S. hospc^s for vjgggis yearg 990 1995 2000 

y 6876 7123 7123 6965 6872 6649 6291 5810 

(a) Find a quadratic regression line to fit this data. 

(b) Use the model to determine the maximum number of hospitals. 

(c) In which year was this? 

(d) In what years were there approximately 7,000 hospitals? 

(e) What seems to be the trend with this data? 

57. A pendu^m^p distance is measured and recorded in the following table. 5 q 

length 25 16.25 10.563 6.866 4.463 2.901 

(a) What seems to be the best model for this data? 

(b) Find a quadratic regression line to fit this data. Approximate the length of the seventh swing. 

(c) Find an exponential regression line to fit this data. Approximate the length of the seventh 
swing. 



10.10 Chapter 10 Test 



1. True or false? The vertex determines the domain of the quadratic function. 

2. Suppose the leading coefficient a = -|. What can you conclude about the shape of the parabola? 

3. Find the discriminant of the equation and determine the number of real solutions: = -2x 2 + 3x- 2. 

4. A ball is thrown upward from a height of four feet with an initial velocity of 45 feet/second. 

(a) Using Newton's law, write the equation to model this situation. 

(b) What is the maximum height of the ball? 

(c) When will the ball reach 10 feet? 

(d) Will the ball ever reach 36.7 feet? 

(e) When will the ball hit the ground? 

In 5-9, solve the equation using any method. 



5. 


2x 2 = 2x + 40 


6. 


llf = j + 24 


7. 


8 2 = l 


8. 


llr 2 - 5 = -178 


9. 


x 2 + 8x - 65 = - 



10. What is the vertex of y = —{x - 6) + 5? Does the parabola open up or down? Is the vertex a 
maximum or a minimum? 

11. Graph y= (x + 2) 2 -3. 

12. Evaluate the discriminant. How many real solutions do the quadratic equation have? -5x 2 - 6x = 1 

13. Suppose D = -14. What can you conclude about the solutions to the quadratic equation? 

14. Rewrite in standard form: y - 7 = -2{x + l) 2 . 

15. Graph and determine the function's range and vertex: y = -x 2 + 2x - 2. 

16. Graph and determine the function's range and y-intercept: y = ^x 2 + 4x + 5. 

17. The following information was taken from USA Today regarding the number of cancer deaths for 
various years. 



www.ckl2.org 420 



Table 10.8: 



Year Number of Deaths Per 100,000 men 

1980 205.3 

1985 212.6 

1989 217.6 

1993 212.1 

1997 201.9 



Cancer Deaths of Men (Source: USA Today) 

(a) Find a linear regression line to fit this data. Use it to predict the number of male deaths caused by 
cancer in 1999. 

(b) Find a linear regression line to fit this data. Use it to predict the number of male deaths caused by 
cancer in 1999. 

(c) Find an exponential regression line to fit this data, to predict the number of male deaths caused by 
cancer in 1999. 

(d) Which seems to be the best fit for this data? 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www .ckl2. org/fl exr/chapt er/9620 . 



421 www.ckl2.org 



Chapter 11 

Radicals and Geometry 
Connections; Data Analysis 



Radicals in mathematics are important. By using radicals as inverse operations to exponents, you can 
solve almost any exponential equation. Radicals such as the square root have been used for thousands 
of years. Square roots are extremely useful in geometry by finding the hypotenuse of a right triangle or 
solving for the side length of a square. 

In this chapter you will learn the basics of radicals and apply these basics to geometry concepts, such as 
Pythagorean's Theorem, the Distance Formula, and the Midpoint Formula. The last several sections of 
this chapter will discuss data analysis, a method used to analyze data by creating charts and graphs. 




11.1 Graphs of Square Root Functions 

You have used squared roots many times in this text: to simplify, to evaluate, and to solve. This lesson 
will focus on the graph of the square root function. 

The square root function is defined by f(x) = ^x-h + /:, where x - h > and (h, k) represents the origin 
of the curve. 

The graph of the parent function f(x) = ^fx is shown below. The function is not defined for negative 
values of x; you cannot take the square root of a negative number and get a real value. 



www.ckl2.org 



422 



f(X 


^ = v 


x 
















































































































































































































































































































- 































: 
























































































































































































































































































By shifting the square root function around the coordinate plane, you will change the origin of the curve. 

Example: Graph f(x) = ^fx + 4 and compare it to the parent function. 

Solution: This graph has been shifted vertically upward four units from the parent function f(x) = V*- 
The graph is shown below. 







+4 






















































































































































































































































































S 










































, 








































































































































































5 


















: 












i 



















































Graphing Square Root Functions Using a Calculator 



Graphing square root functions is similar to graphing linear, quadratic, or exponential functions. Use the 
following steps: 

These figures should be side by side. Due to the captions, they have moved in a vertical alignment. 
Ploti Plots Mot3 

vYi = 
^Ys = 



423 



www.ckl2.org 



WINDOW 
Xnin=0 
Xnax=2Q 
Xscl=l 
Vnin=0 
Vnax=10 
Vscl=l 
Xres=l 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Graphs of Square Root Functions (15:01) 




Figure 11.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/815 



1. In the definition of a square root function, why must (x - h) > 0? 

2. What is the domain and range of the parent function f(x) = ^Jxl 

Identify the ordered pair of the origin of each square root function. 



3. /(*) = V^2 

4. g{x) = V* + 4 + 6 

5. h(x) = Vx^I-l 

6. y = V^ + 3 

7. f{x) = V2x + 4 



Graph the following functions on the same coordinate axes. 

8. y = yfx, y = 2.5 ^fx 1 and y = -2.5 V* 

9. y = yfx, y = 0.3 V*> an d y = 0.6 ^[x 
10. y = V*> y = V* - 5, and y = y/x + 5 



www.ckl2.org 



424 



11. y = V^> y — V^ + 8, and y = V* ~ ■ 
In 12-20, graph the function. 



12. y= V2jc-1 

13. y = V4x + 4 

14. y = V5-x 

15. y = 2V^+5 

16. y = 3 - V* 

17. y = 4 + 2y^ 

18. y = 2 V2jc + 3 + 1 

19. 3; = 4 + 2V2-x 



20. y= V*TT- Vi^5 

21. The length between any two consecutive bases of a baseball diamond is 90 feet. How much shorter is 
it for the catcher to walk along the diagonal from home plate to second base than the runner running 
from second to home? 

22. The units of acceleration of gravity are given in feet per second squared. It is g = 32 ft/ s 2 at sea 
level. Graph the period of a pendulum with respect to its length in feet. For what length in feet will 
the period of a pendulum be two seconds? 

23. The acceleration of gravity on the Moon is 1.6 m/s 2 . Graph the period of a pendulum on the Moon 
with respect to its length in meters. For what length, in meters, will the period of a pendulum be 
10 seconds? 

24. The acceleration of gravity on Mars is 3.69 m/s 2 . Graph the period of a pendulum on Mars with 
respect to its length in meters. For what length, in meters, will the period of a pendulum be three 
seconds? 

25. The acceleration of gravity on the Earth depends on the latitude and altitude of a place. The value 
of g is slightly smaller for places closer to the Equator than places closer to the Poles, and the value 
of g is slightly smaller for places at higher altitudes that it is for places at lower altitudes. In Helsinki, 
the value of g = 9.819 m/s 2 , in Los Angeles the value of g = 9.796 m/s 2 , and in Mexico City the value 
of g = 9.779 m/s 2 . Graph the period of a pendulum with respect to its length for all three cities on 
the same graph. Use the formula to find the length (in meters) of a pendulum with a period of 8 
seconds for each of these cities. 

26. The aspect ratio of a wide-screen TV is 2.39:1. Graph the length of the diagonal of a screen as a 
function of the area of the screen. What is the diagonal of a screen with area 150 in 2 ? 

Graph the following functions using a graphing calculator. 

27. y = V3l ^2 

28. y = 4 + V2 - x 

29. y = V;t 2 -9 

30. y = V*- V*T2 

Mixed Review 

31. Solve 16 = 2jc 2 -3jc + 4. 

32. Write an equation for a line with slope of 0.2 containing the point (1, 10). 

33. Are these lines parallel, perpendicular, or neither: x + 5y = 16 and y = 5x - 3? 

34. Which of the following vertices minimizes the expression 20x + 32y? 

(a) (50, 0) 

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(b) (0, 60) 

(c) (15, 30) 

35. Is the following graph a function? Explain your reasoning 



Ux 


M 


f-Z 


































9<x 


\=- 


jx-Z 










































































































































































































/ 
























5 












' 


V 




\ 










1 -J 




























































































*r- 





























36. Between which two consecutive integers is V205? 



11.2 Radical Expressions 

Radicals are the roots of values. In fact, the word radical comes from the Latin word "radix," meaning 
"root." You are most comfortable with the square root symbol ^fx; however, there are many more radical 
symbols. 

A radical is a mathematical expression involving a root by means of a radical sign. 



^/y = x 


because x 3 = y 


A/27 = 3, because 3 3 = 27 


i/y = x 


because x 4 = y 


^16 = 2 because 2 4 = 16 


rfy = x 


because x n = y 





Some roots do not have real values; in this case, they are called undefined. 

Even roots of negative numbers are undefined. 

ifx is undefined when n is an even whole number and x < 0. 

Example 1: Evaluate the following radicals: 

• ^64 
. ^=81 

Solution: ^^64 = 4 because 4 3 = 64 

V-81 is undefined because n is an even whole number and -81 < 0. 

In Chapter 8, you learned how to evaluate rational exponents: 

X 

ay where x = power and y = root 

This can be written in radical notation using the following property. 
Rational Exponent Property: For integer values of x and whole values of y: 



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426 



ay = ya 



Example: Rewrite x§ using radical notation. 

Solution: This is correctly read as the sixth root of x to the fifth power. Writing in radical notation, 
X 6 = Vx^, where x 5 > 0. 

Example 2: Evaluate Vi?. 

Solution: This is read, "The fourth root of four to the second power." 

4 2 = 16 

The fourth root of 16 is 2; therefore, 

^42 = 2 

In Chapter 1, Lesson 5, you learned how to simplify a square root. You can also simplify other radicals, 
like cube roots and fourth roots. 

Example: Simplify Vl35. 

Solution: Begin by finding the prime factorization of 135. This is easily done by using a factor tree. 

135 




^135= ^3 • 3 • 3 • 5 = ^33- ^5 

3^5 

Adding or Subtracting Radicals 

To add or subtract radicals, they must have the same root and radicand. 

a\[x + b-s/x = (a + b)\[x 

Example 3: Add 3 V5 + 6 V5. 

Solution: The value " V5" is considered a like term. Using the rule above, 

3V5 + 6V5 = (3 + 6)V5 = 9V5 

Example: Simplify 2 ^13 + 6 ^12. 

Solution: The cube roots are not like terms, therefore there can be no further simplification. 

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In some cases, the radical may need to be reduced before addition/subtraction is possible. 
Example 4: Simplify 4 V3 + 2 Vl2. 
Solution: ^fl2 simplifies as 2 V3. 

4V3 + 2VT2^4V3 + 2(2V3) 
4V3 + 4V3 = 8V3 

Multiplying or Dividing Radicals 

To multiply radicands, the roots must be the same. 

Example: Simplify V3 • ^fl2. 

Solution: V3 • Vl2 = V36 = 6 

Dividing radicals is more complicated. A radical in the denominator of a fraction is not considered simplified 
by mathematicians. In order to simplify the fraction, you must rationalize the denominator. 

To rationalize the denominator means to remove any radical signs from the denominator of the fraction 
using multiplication. 

Remember: ^ x Vfl=V^ = a 

Example 1: Simplify A=. 

Solution: We must clear the denominator of its radical using the property above. Remember, what you 
do to one piece of a fraction, you must do to all pieces of the fraction. 



V3 2V3 2V3 



V3 X V3 V32 3 

Example: Simplify -J=. 

Solution: In this case, we need to make the number inside the cube root a perfect cube. We need to 
multiply the numerator and the denominator by v5 2 . 

J_ jg _ 7 3 V25 _ 7 3 V25 



Real- World Radicals 

Example: A pool is twice as long as it is wide and is surrounded by a walkway of uniform width of 1 foot. 
The combined area of the pool and the walkway is 400 square-feet. Find the dimensions of the pool and the 
area of the pool. 





2x 




1 ft 
<-> 




X 




$m 





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428 



Solution: 

1. Make a sketch. 

2. Let x = the width of the pool. 

3. Write an equation. Area = length • width 

Combined length of pool and walkway = 2x + 2 
Combined width of pool and walkway = x + 2 

Area= (2* + 2)(* + 2) 

Since the combined area of pool and walkway is 400 ft 2 we can write the equation. 

(2x + 2)(x + 2) =400 

4- Solve the equation: 

(2x + 2)(x + 2) =400 
Multiply in order to eliminate the parentheses. 2x + 4x + 2x + 4 = 400 

Collect like terms. 2x 2 + 6x + 4 = 400 

Move all terms to one side of the equation. 2x 2 + 6x - 396 = 

Divide all terms by 2. x 2 + 3x - 198 = 



-b± V& 2 - 4<2c 
2o 



-3+ V3 2 -4(l)(-198) 

2(1) 
-3 ± V80l -3 ± 28.3 



2 2 

Use the Quadratic Formula, x « 12.65 or -15.65 feet 

5. We can disregard the negative solution since it does not make sense for this context. Thus, we 
can check our answer of 12.65 by substituting the result in the area formula. 

Area = [2(12.65) + 2)] (12.65 + 2) = 27.3 • 14.65 « 400 ft 2 . 
The answer checks out. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Radical Expressions with Higher Roots (8:46) 

CK-12 Basic Algebra: More Simplifying Radical Expressions (7:57) 

CK-12 Basic Algebra: How to Rationalize a Denominator (10:18) 

429 www.ckl2.org 




Figure 11.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/816 



Video 



Figure 11.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/817 




Figure 11.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/818 



www.ckl2.org 



430 



1. For which values of n is "ty-16 undefined? 
Evaluate each radical expression. 

2. Vl69 

3. ffisi 

4. ^-125 

5. Vl024 

Write each expression as a rational exponent. 

5. ^14 

6. -^ivv 

7. V^ 



Write the following expressions in simplest radical form. 

9. V24 

10. V300 

11. ^96 

19 / 240 
1Z ' V 567 

13. ^500 

14. ^64x 8 

15. % 48a 3 b 7 

16 - -Vi357 

17. Trae or /afee? ^5-^6 = 4 -\/30 

Simplify the following expressions as much as possible. 



17. 3V8-6V32 

18. VI80 + 6V405 

19. V6-V27 + 2V54 + 3V48 

20. V&t3-4xV98lc 

21. Vi8a+ V27a 

22. \^3 + xa/256 



Multiply the following expressions. 

23. V6(VlO+ V8) 

24. (Va- V&)(V« + V5) 

25. (2Vx + 5)(2Vx + 5) 

Rationalize the denominator. 



26. 



/15 



431 



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27. -9= 
Vio 

28. -?£- 

29. -# 

30. The volume of a spherical balloon is 950cm 3 . Find the radius of the balloon. (Volume of a sphere 

31. A rectangular picture is 9 inches wide and 12 inches long. The picture has a frame of uniform width. 
If the combined area of picture and frame is 180m 2 , what is the width of the frame? 

32. The volume of a soda can is 355 cm 3 . The height of the can is four times the radius of the base. Find 
the radius of the base of the cylinder. 

Mixed Review 

33. An item originally priced $c is marked down 15%. The new price is $612.99. What is c? 

34. Solve *±2 = 21. 

35. According to the Economic Policy Institute (EPI), minimum wage in 1989 was $3.35 per hour. In 
2009, it was $7.25 per hour. What is the average rate of change? 

36. What is the vertex of y = 2(jc + l) 2 + 4? Is this a minimum or a maximum? 

37. Using the minimum wage data (adjusted for inflation) compiled from EPI, answer the following 
questions. 

(a) Graph the data as a scatter plot. 

(b) Which is the best model for this data: linear, quadratic, or exponential? 

(c) Find the model of best fit and use it to predict minimum wage adjusted for inflation for 1999. 

(d) According to EPI, the 1999 minimum wage adjusted for inflation was $6.58. How close was your 
model? 

(e) Use interpolation to find minimum wage in 1962. 

Table 11.1: 

Year Minimum Wage Adj. Year Minimum Wage Adj. 

for Inflation for Inflation 

1947 3.40 1952 5.36 

1957 6.74 1960 6.40 

1965 7.52 1970 7.81 

1978 7.93 1981 7.52 

1986 6.21 1990 6.00 

1993 6.16 1997 6.81 

2000 6.37 2004 5.80 

2006 5.44 2008 6.48 

2009 7.25 



11.3 Radical Equations 



Solving radical equations is no different from solving linear or quadratic equations. Before you can begin 
to solve a radical equation, you must know how to cancel the radical. To do that, you must know its 
inverse. 



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Table 11.2: 



Original Operation Inverse Operation 

Cube Root Cubing (to the third power) 

Square Root Squaring (to the second power) 

Fourth Root Fourth power 

"nth" Root "nth" power 



To solve a radical equation, you apply the solving equation steps you learned in previous chapters, including 
the inverse operations for roots. 

Example 1: Solve V2x - 1 = 5. 

Solution: The first operation that must be removed is the square root. Square both sides. 

( V2jc - l) 2 = 5 2 

2x - 1 = 25 

2x = 26 

x= 13 



Remember to check your answer by substituting it into the original problem to see if it makes sense. 

Example: Solve V* + 15 = V3x - 3. 

Solution: Begin by canceling the square roots by squaring both sides. 

( V^Tl5) 2 = ( V3jc - 3) 2 
x + 15 = 3x - 3 
Isolate the x - variable : 18 = 2x 

x = 9 

Check the solution: V9 + 15 = 73(9) - 3 -> V24 = V24. The solution checks. 

Extraneous Solutions 

Not every solution of a radical equation will check in the original problem. This is called an extraneous 
solution. This means you can find a solution using algebra, but it will not work when checked. This is 
because of the rule in Lesson 11.2. 

Even roots of negative numbers are undefined. 

Example: Solve V* - 3 - yfx = 1. 
Solution: 

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Isolate one of the radical expressions. Vx - 3 = V* + 1 

Square both sides. ( Vx - 3 J = ( V* + l) 

Remove parentheses. x - 3 = ( V*) + 2 V* + 1 

Simplify. x - 3 = x -\- 2^ -\- 1 
Now isolate the remaining radical. - 4 = 2 V* 

Divide all terms by 2. - 2 = V* 

Square both sides. x = 4 

Check: V4 - 3 - V4 = VT-2 = l-2 = -l. The solution does not check out. The equation has no real 
solutions. Therefore, x = 4 is an extraneous solution. 

Radical Equations in Real Life 

Example: A sphere has a volume of 456 cm 3 . If the radius of the sphere is increased by 2 cm, what is the 
new volume of the sphere? 




Solution: 

1. Define variables. Let R = the radius of the sphere. 



2. Find an equation. The volume of a sphere is given by the formula: V = -^nr . 

By substituting 456 for the volume variable, the equation becomes 456 = |7rr 3 

Multiply by 3. 1368 = 4;rr 3 

Divide by 4tt. 108.92 = r 3 

Take the cube root of each side. r = a/108.92 =^> r = 4.776 cm 

The new radius is 2 centimeters more. r = 6.776 cm 

The new volume is : V = -tt(6.776) 3 = 1302.5 cm 3 

o 



Check by substituting the values of the radii into the volume formula. 
V = |7rr 3 = f7r(4.776) 3 = 456 cm 3 . The solution checks out. 

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Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Extraneous Solutions to Radical Equations (11:10) 




Figure 11.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/819 



CK-12 Basic Algebra: Radical Equation Examples (5:16) 




Figure 11.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/820 

CK-12 Basic Algebra: More Involved Radical Equation Example (11:54) 




Figure 11.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/821 

In 1-16, find the solution to each of the following radical equations. Identify extraneous solutions. 



1. VxT2- 2 = 

2. V 3jc - 1 = 5 

3. 2V4^3x + 3 = 



435 



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4. 


Vx - 3 = 1 


5. 


\^x 2 - 9 = 2 


6. 


V-2 - 5x + 3 = 


7. 


Vx = x - 6 


8. 


Vx 2 - 5x - 6 = 


9. 


V(x+l)(x-3) = x 


10. 


Vx + 6 = x + 4 


11. 


Vx = Vx - 9 + 1 


12. 


V3x + 4 = -6 


13. 


Vl0-5x+ Vl-x = 7 


14. 


V2x -2-2V*" + 2 = 


15. 


V2x + 5 - 3 V2x - 3 = V2 - x 


16. 


3 Vx - 9 = V2x - 14 



17. The area of a triangle is 24 in 2 and the height of the triangle is twice as long and the base. What are 
the base and the height of the triangle? 

A(h) 

18. The volume of a square pyramid is given by the formula V = -^, where A = area of the base and 
h = height of the pyramid. The volume of a square pyramid is 1,600 cubic meters. If its height is 10 
meters, find the area of its base. 

19. The volume of a cylinder is 245 cm 3 and the height of the cylinder is one-third the diameter of the 
cylinder's base. The diameter of the cylinder is kept the same, but the height of the cylinder is 
increased by two centimeters. What is the volume of the new cylinder? (Volume = nr 2 • h) 

20. The height of a golf ball as it travels through the air is given by the equation h = -16t 2 + 256. Find 
the time when the ball is at a height of 120 feet. 



Mixed Review 



21. Joy sells two types of yarn: wool and synthetic. Wool is $12 per skein and synthetic is $9 per skein. 
If Joy sold 16 skeins of synthetic and collected a total of 432, how many skeins of wool did she sell? 

22. Solve 16>|jc-4|. 

[y < 2x - 4 

23. Graph the solution < , 

\y>-\x + 6 

24. You randomly point to a day in the month of February 2011. What is the probability your finger 
lands on a Monday? 

25. Carbon-14 has a half life of 5,730 years. Your dog dug a bone from your yard. It had 93% carbon-14 
remaining. How old is the bone? 

26. What is true about solutions to inconsistent systems? 



11.4 The Pythagorean Theorem and its Converse 

One of the most important theorems in history is Pythagorean's Theorem. Simply put, it states, "The 
sum of the square of each leg of a right triangle is equal to the square of the hypotenuse." 

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Leg :b 




hypotenuse 
c 



Let's review basic right triangle anatomy. 

The two segments forming the right angle (90°) are called the legs of the right triangle. The segment 
opposite the right angle is called the hypotenuse. 

So, the Pythagorean Theorem states, (leg^ 2 + (leg 2 ) 2 = (hypotenuse) 2 : 

2 , 7 2 2 

a + b = c 



Or, to find the hypotenuse, c = V<2 2 + b 2 . 

Notice this relationship is only true for right triangles. In later courses, you will learn how to determine 
relationships with non-right triangles. 

Although we usually refer to the Pythagorean Theorem when determining side lengths of a right triangle, 
the theorem originally made a statement about areas. If we build squares on each side of a right triangle, 
the Pythagorean Theorem says that the area of the square whose side is the hypotenuse is equal to the 
sum of the areas of the squares formed by the legs of the triangle. 



1 

_U 

a 



Multimedia Link: For an interactive version of Pythagorean's Theorem, use this Shockwave http: 
//www. pbs . org/wgbh/nova/pr oof /puzzle/theorem, html - applet produced by NOVA and PBS. 



The Converse of Pythagorean's Theorem 

The Converse of the Pythagorean Theorem is also true. That is, if the lengths of three sides of a 
triangle make the equation a 2 + b 2 = c 2 true, then they represent the sides of a right triangle. 

With this converse, you can use the Pythagorean Theorem to prove that a triangle is a right triangle, even 
if you do not know any of the triangle's angle measurements. 

Example: Does the triangle below contain a right angle? 



437 



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17 ft. 



Solution: This triangle does not have any right angle marks or measured angles, so you cannot assume you 
know whether the triangle is acute, right, or obtuse just by looking at it. Take a moment to analyze the 
side lengths and see how they are related. Two of the sides, 15 and 17, are relatively close in length. The 
third side, 8, is about half the length of the two longer sides. 

To see if the triangle might be right, try substituting the side lengths into the Pythagorean Theorem to 
see if they makes the equation true. The hypotenuse is always the longest side, so 17 should be substituted 
for c. The other two values can represent a and b and the order is not important. 

a 2 + b 2 = c 2 
8 2 + 15 2 = 17 2 
64 + 225 = 289 
289 = 289 

Since both sides of the equation are equal, these values satisfy the Pythagorean Theorem. Therefore, the 
triangle described in the problem is a right triangle. 

Example: One leg of a right triangle is 5 more than the other leg. The hypotenuse is one more than twice 
the size of the short leg. Find the dimensions of the triangle. 

Solution: Let x = length of the short leg. Then, x + 5 = length of the long leg and 2x + 1 = length of the 
hypotenuse. 




x+5 

The sides of the triangle must satisfy the Pythagorean Theorem. 

Therefore, x 2 + (x + 5) 2 = (2jc + 1) 

Eliminate the parentheses. x 2 + x 2 + lOx + 25 = 4x 2 + 4x + 1 

Move all terms to the right hand side of the equation. = 2x 2 - 6x - 24 

Divide all terms by 2. = x 2 - 3x - 12 



Solve using the Quadratic Formula. 



3+ V9T48 3+ V57 

X= 2 = ^^ 

x « 5.27 or x « -2.27 



The negative solution does not make sense in the context of this problem. So, use x = 5.27 and we get 
short - leg = 5.27, long - leg = 10.27 and hypotenuse = 11.54. 

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Real- World Right Triangles 

Example: Find the area of the shaded region in the following diagram. 




Solution: 

Draw the diagonal of the square on the figure. 




Notice that the diagonal of the square is also the diameter of the circle. 
Define variables. Let c = diameter of the circle. 

2 2 + 2 2 = c 2 



Write the formula and solve. 



4 + 4 = c z 

.2 _ Q 



V8: 



2V2 



The diameter of the circle is 2 V2. Therefore, the radius is r = V2. 

Area of a circle is A = nr 2 = n ( V2 J = 2n. 

Area of the shaded region is therefore 2n - 4 « 2.28. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Pythagorean Theorem (13:03) 

Verify that each triangle is a right triangle. 

1. a = 12, b = 9,c = 15 

2. a = 6, b = 6, c = 6V2 

3. a = 8, Z? = 8V3, c = 16 



Find the missing length of each right triangle. 



439 



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Figure 11.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/822 



4. a = 12, b = 16, c =? 

5. a =?, Z? = 20, c = 30 

6. fl = 4, &=?, c= 11 

7. 





10. One leg of a right triangle is 4 feet less than the hypotenuse. The other leg is 12 feet. Find the 
lengths of the three sides of the triangle. 

11. One leg of a right triangle is 3 more than twice the length of the other. The hypotenuse is 3 times 
the length of the short leg. Find the lengths of the three legs of the triangle. 

12. A regulation baseball diamond is a square with 90 feet between bases. How far is second base from 
home plate? 

13. Emanuel has a cardboard box that measures 20 cm x 10 cm x 8 cm(length x width x height). What is 
the length of the diagonal from a bottom corner to the opposite top corner? 

14. Samuel places a ladder against his house. The base of the ladder is 6 feet from the house and the 
ladder is 10 feet long. How high above the ground does the ladder touch the wall of the house? 

15. Find the area of the triangle if area of a triangle is defined as A = ^ base x height. 




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440 



16. Instead of walking along the two sides of a rectangular field, Mario decided to cut across the diagonal. 
He saves a distance that is half of the long side of the field. Find the length of the long side of the 
field given that the short side is 123 feet. 

17. Marcus sails due north and Sandra sails due east from the same starting point. In two hours, Marcus's 
boat is 35 miles from the starting point and Sandra's boat is 28 miles from the starting point. How 
far are the boats from each other? 

18. Determine the area of the circle. 




19. In a right triangle, one leg is twice as long as the other and the perimeter is 28. What are the 
measures of the sides of the triangle? 

20. Maria has a rectangular cookie sheet that measures 10 inches x 14 inches. Find the length of the 
diagonal of the cookie sheet. 

21. Mike is loading a moving van by walking up a ramp. The ramp is 10 feet long and the bed of the 
van is 2.5 feet above the ground. How far does the ramp extend past the back of the van? 

Mixed Review 

22. A population increases by 1.2% annually. The current population is 121,000. 

(a) What will the population be in 13 years? 

(b) Assuming this rate continues, when will the population reach 200,000? 

23. Write 1.29651843 • 10 5 in standard form. 

24. Is 4, 2, 1, ^, g, i, ... an example of a geometric sequence? Explain your answer. 

25. Simplify 6x 3 (4 xy 2 +yh). 

26. Suppose = (jc - 2)(x + l)(x - 3). What are the x-intercepts? 

27. Simplify V300. 

Quick Quiz 

1. Identify the origin of h(x) = V* - 2 + 5, then graph the function. 

2. Simplify -$= by rationalizing the denominator. 



3. Simplify: V-32. If the answer is not possible, explain why. 

4. What is an extraneous solution? In what situations do such solutions occur? 

5. Can 3, 4, 6 form a right triangle? 

6. Solve 5 = WT6. 

11.5 The Distance and Midpoint Formulas 

You have already learned you can use the Pythagorean Theorem to understand different types of right 
triangles and find missing lengths. This lesson will expand its use to include finding the distance between 
two points on a Cartesian plane. 

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The Distance Formula 

Look at the points on the grid below. Find the length of the segment connecting (1, 5) and (5, 2). 




The question asks you to identify the length of the segment. Because the segment is not parallel to either 
axis, it is difficult to measure given the coordinate grid. 

However, it is possible to think of this segment as the hypotenuse of a right triangle. Draw a vertical line 
and a horizontal line. Find the point of intersection. This point represents the third vertex in the right 
triangle. 









5" 


i 


[(1,5] 


















— *- 
— 3" 






















, 1 










— 1- 




(1,2) 




<5,2) 




j— 1— 


— M 


— 1— 


^M 


i — | — 


— M 


h- 1— 




! 


h— f 
i 










i 


t 













You can easily count the lengths of the legs of this triangle on the grid. The vertical leg extends from (1, 
2) to (1, 5), so it is |5 - 2| = |3| = 3 units long. The horizontal leg extends from (1, 2) to (5, 2), so it is 
|5 — 1| = |4| = 4 units long. Use the Pythagorean Theorem with these values for the lengths of each leg to 
find the length of the hypotenuse. 

a 2 + b 2 = c 2 

3 2 + 4 2 = c 2 

9 + 16 = c 2 

25 = c 2 

V25= V? 

5 = c 



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442 



The segment connecting (1, 5) and (5, 2) is 5 units long. 

Mathematicians have simplified this process and created a formula that uses these steps to find the distance 
between any two points in the coordinate plane. If you use the distance formula, you don't have to draw 
the extra lines. 

Distance Formula: Given points (xi,yi) and (^2,^2), the length of the segment connecting those two 

points is d = VCV2 ~yi) 2 + (*2 ~ x\) 2 

Example 1: Find the distance between (-3, 5) and (4, -2). 

Solution: Use the Distance Formula. Let (xi,yi) = (-3,5) and (^2,^2) = (4,-2). 

d= > /(- 2 -5)2 + (4-(-3))2-> ^" 7 ) 2 + 72 
d = V98 = 7 V2 units 

Example: Point A = (6, -4) and point B = (2,k). What is the value of k such that the distance between the 
two points is 5? 

Solution: Use the Distance Formula. 

d= ^(yi-y2) 2 + {xi-x 2 y^h= ^(4-^)2 + (6 -2)2 



Square both sides of the equation. 

Simplify. 
Eliminate the parentheses. 
Simplify. 

Find k using the Quadratic Formula. 



5 2 = 



<y/(4 -*) 2 + (6 -2)2 
25 = (-4 - kf + 16 



= JT + 8*+16-9 

= k 2 + 8k + 7 
, -8± V64 - 28 

K = = 



-8 ± V36 -8 ± 6 



k — -7 or k — -1. There are two possibilities for the value of k. Let's graph the points to get a visual 
representation of our results. 

















y, 


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Example: At 8 a.m. one day, Amir decides to walk in a straight line on the beach. After two hours of 
making no turns and traveling at a steady rate, Amir was two mile east and four miles north of his starting 
point. How far did Amir walk and what was his walking speed? 











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Solution: Plot Amir's route on a coordinate graph. We can place his starting point at the origin A = (0,0). 
Then, his ending point will be at point B = (2,4). The distance can be found with the Distance Formula. 

d= ^(4 - 0) 2 + (2 - 0) 2 = ^/(4) 2 + (2) 2 + Vl6T4= V20 
d = 4.47 miles. 



Since Amir walked 4.47 miles in 2 hours, his speed is: 

4.47 miles 

Speed = — 

2 hours 



2.24 mi/h 



The Midpoint Formula 

Consider the following situation: You live in Des Moines, Iowa and your grandparents live in Houston, 
Texas. You plan to visit them for the summer and your parents agree to meet your grandparents halfway 
to exchange you. How do you find this location? 

By meeting something "halfway," you are finding the midpoint of the straight line connecting the two 
segments. In the above situation, the midpoint would be halfway between Des Moines and Houston. 

The midpoint between two coordinates represents the halfway point, or the average. It is an ordered 
pair (x m ,y m ). 

_ (xi + x 2 ) (yi +V2) 

Example: Des Moines, Iowa has the coordinates (41.59, 93.62). 

Houston, Texas has the coordinates (29.76, 95.36). 

Find the coordinates of the midpoint between these two cities. 

Solution: Decide which ordered pair will represent (x±,yi) and which will represent (x2,j2)- 

(jci,yi) = (41.59,93.62) 
(jc 2 ,y 2 ) = (29.76,95.36) 



www.ckl2.org 



444 



Compute the midpoint using the formula {x m ,y i 



(xi+x 2 ) (yi+j2) 



y^m^yn 



2 ' 2 

(41.59 + 29.76) (93.62 + 95.36) 



(xm,y m ) = (35.675,94.49) 



Using Google Maps, you can meet in the Ozark National Forest, halfway between the two cities. 
Example 2: A segment with endpoints (9, -2) and (jci,yi) has a midpoint of (2, -6). Find (jti,yi). 

x m 



Solution: Use the Midpoint Formula. ^ Xl X2 > 



2 = -^ > 4 = Xl + ! 

xi = -5 



Following the same ^— ^ — - 



-6 -> yi + (-2) = -12 



yi = -10 
(*i,yi) = (-5,-10) 



Practice Set 



Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Distance Formula (9:39) 




Figure 11.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/823 

CK-12 Basic Algebra: Midpoint Formula (6:41) 

CK-12 Basic Algebra: Visual Pythagorean Theorem Proof (8:50) 

CK-12 Basic Algebra: Pythagorean Theorem 3 (3:00) 

In 1-10, find the distance between the two points. 



1. (xi,yi) and (x 2 ,y 2 ) 

2. (7, 7) and (-7, 7) 

3. (-3, 6) and (3, -6) 

4. (-3, -1) and (-5, -i 



445 



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Figure 11.10: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/824 



Video 



Figure 11.11: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/825 




Figure 11.12: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/826 



www.ckl2.org 



446 



5. (3, -4) and (6, 0) 

6. (-1, 0) and (4, 2) 

7. (-3, 2) and (6, 2) 

8. (0.5, -2.5) and (4, -4) 

9. (12, -10) and (0, -6) 

10. (2.3, 4.5) and (-3.4, -5.2) 

11. Find all points having an x-coordinate of -4 and whose distance from point (4, 2) is 10. 

12. Find all points having a v-coordinate of 3 and whose distance from point (-2, 5) is 8. 

In 13-22, find the midpoint of the line segment joining the two points. 

13. (xi,yi) and (x 2 ,y 2 ) 

14. (7, 7) and (-7, 7) 

15. (-3, 6) and (3, -6) 

16. (-3, -1) and (-5, -8) 

17. (3, -4) and (6, 1) 

18. (2, -3) and (2, 4) 

19. (4, -5) and (8, 2) 

20. (1.8, -3.4) and (-0.4, 1.4) 

21. (5, -1) and (-4, 0) 

22. (10, 2) and (2, -4) 

23. An endpoint of a line segment is (4, 5) and the midpoint of the line segment is (3, -2). Find the 
other endpoint. 

24. An endpoint of a line segment is (-10, -2) and the midpoint of the line segment is (0, 4). Find the 
other endpoint. 

25. Michelle decides to ride her bike one day. First she rides her bike due south for 12 miles, then the 
direction of the bike trail changes and she rides in the new direction for a while longer. When she 
stops, Michelle is 2 miles south and 10 miles west from her starting point. Find the total distance 
that Michelle covered from her starting point. 

26. Shawn lives six blocks west and ten blocks north of the center of town. Kenya lives fourteen blocks 
east and two blocks north of the center of town. 

(a) How far apart are these two girls "as the crow flies"? 

(b) Where is the halfway point between their houses? 

Mixed Review 

27. Solve (x-4) 2 = 121. 

28. What is the GCF of 21ab 4 and 15a 7 Z> 2 ? 

29. Evaluate 10C7 and explain its meaning. 

30. Factor 6x 2 + 17x + 5. 

31. Find the area of a rectangle with a length of (16 + 2m) and a width of (12 + 2m). 

32. Factor x 2 - 81. 

11.6 Measures of Central Tendency and Disper- 
sion 

The majority of this textbook centers upon two-variable data, data with an input and an output. This 
is also known as bivariate data. There are many types of situations in which only one set of data is 

447 www.ckl2.org 



given. This data is known as univariate data. Unlike data you have seen before, no rule can be written 
relating univariate data. Instead, other methods are used to analyze the data. Three such methods are 
the measures of central tendency. 

Measures of central tendency are the center values of a data set. 

• Mean is the average of all the data. Its symbol is x. 

• Mode is the data value appearing most often in the data set. 

• Median is the middle value of the data set, arranged in ascending order. 

Example: Mrs. Kramer collected the scores from her students test and obtained the following data: 
90, 76, 53, 78, 88, 80, 81, 91, 99, 68, 62, 78, 67, 82, 88, 89, 78, 72, 77, 96, 93, 88, 88 
Find the mean, median, mode, and range of this data. 
Solution: 

• To find the mean, add all the values and divide by the number of pieces you added. 

mean = 80.96 

• To find the mode, look for the value(s) repeating the most. 

mode = 88 

• To find the median, organize the data from least to greatest. Then find the middle value. 
53, 62, 62, 67, 68, 72, 76, 77, 78, 78, 78, 78, 80, 81, 82, 88, 88, 88, 88, 89, 90, 91, 93, 96, 99 

median = 81 

• To find the range, subtract the highest value and the lowest value. 

range = 99 - 53 = 46 

When a data set has two modes, it is bimodal. 

If the data does not have a "middle value," the median is the average of the two middle values. This 
occurs when data sets have an even number of entries. 

Which Measure Is Best? 

While the mean, mode, and median represent centers of data, one is usually more beneficial than another 
when describing a particular data set. 

For example, if the data has a wide range, the median is a better choice to describe the center than the 
mean. 

• The income of a population is described using the median, because there are very low and very high 
incomes in one given region. 

If the data were categorical, meaning it can be separated into different categories, the mode may be a 
better choice. 

• If a sandwich shop sold ten different sandwiches, the mode would be useful to describe the favorite 
sandwich. 

www.ckl2.org 448 



Measures of Dispersion 

In statistics, measures of dispersion describe how spread apart the data is from the measure of center. 
There are three main types of dispersion: 

• Range - difference between highest and lowest values in data 

• Variance 

• Standard deviation 

Variance is the mean of the squares of the distance each data item (jc*) is from the mean. 



cr 2 



(xi - x) 2 + (x 2 - x) 2 + . . . + (x n - x) 2 



The symbol for variance is cr 2 . 

Example: Find the variance for the following data: 11, 13, 14, 15, 19, 22, 24, 26. 

Solution: First find the mean (x). 

11 + 13 + 14 + 15 + 19 + 22 + 24 + 26 
x= = 18 

It's easier to create a table of the differences and their squares. 

Table 11.3: 



(xi - x 



,2 



11 -7 49 

13 -5 25 

14 -4 16 

15 -3 9 
19 1 1 
22 4 16 
24 6 36 
26 8 64 

Compute the variance: 49+25+16+9+1+16+36+64 = 27 _ 

The variance is a measure of the dispersion and its value is lower for tightly grouped data than for widely 
spread data. In the example above, the variance is 27. What does it mean to say that tightly grouped data 
will have a low variance? You can probably already imagine that the size of the variance also depends on 
the size of the data itself. Below we see ways that mathematicians have tried to standardize the variance. 

The Standard Deviation 

Standard deviation measures how closely the data clusters around the mean. It is the square root of 
the variance. Its symbol is cr. n -^ ; -^ ; it 

_ ^ _ /Ol - X) 2 + (*2 " X) 2 + • • • + {X n ~ X) 



cr = Vcr 



n 
Example 1: Calculate the standard deviation of the previous data set. 



449 www.ckl2.org 



Solution: The standard deviation is the square root of the variance. 

o 2 = 27 so a = 5.196 

Multimedia Link: Watch this http://www.teachertube.com/viewVideo.php?video_id=53143& 
title=How_to_Calculate_the_Standard_Deviation_of _a_Sample - Teacher Tube video for more help 
with standard deviation and variance. 

Example: Find the mean, median, mode, range, variance, and standard deviation of the data set below. 

Table 11.4: 



Address 



Sale Price 



518 CLEVELAND AVE 
1808 MARKESE AVE 
1770 WHITE AVE 

1459 LINCOLN AVE 
1462 ANNE AVE 
2414 DIX HWY 
1523 ANNE AVE 
1763 MARKESE AVE 

1460 CLEVELAND AVE 
1478 MILL ST 



$117,424 

$128,000 

$132,485 

$77,900 

$60,000 

$250,000 

$110,205 

$70,000 

$111,710 

$102,646 



Solution: 



mean — $116,037 

110,205 + 111,710 

median — 

2 

mode — none 
range = $190,000 



$110,957.50 



Use a table to find variance. 



Table 11.5: 






(xi - x) 



117,424 

128,000 

132,485 

77,900 

60,000 

250,000 

110,205 

70,000 

111,710 

102,646 



1387 

11,963 

16,448 

-38,137 

-56,037 

133,963 

-5832 

-46,037 

-4327 

-13,391 



1,923,769 

143,113,369 

270,536,704 

1,454,430,769 

3,140,145,369 

1.7946 x 10 10 

34,012,224 

2,119,405,369 

18,722,929 

179,318,881 



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450 



variance = 2, 530, 769, 498 
standard deviation = 50,306.754 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Average or Central Tendency: Arithmetic Mean, Median, and Mode (9:01) 




Figure 11.13: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/827 

CK-12 Basic Algebra: Range, Variance, and Standard Deviation as Measures of Dispersion (12:34) 




Figure 11.14: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/828 



1. Define measures of central tendency. What are the three listed in this lesson? 

2. Define median. Explain its difference from the mean. In which situations is the median more effective 
to describe the center of the data? 

3. What is bimodal? Give an example of a set of data that is bimodal. 

4. What are the three measures of dispersion described in this lesson? Which is the easiest to compute? 

5. Give the formula for variance and define its variables. 

6. Why may variance be difficult to use as a measure of spread? Use the housing example to help you 
explain. 

7. Describe standard variation. 

8. Explain why the standard deviation of 2, 2, 2, 2, 2, 2, 2, is zero. 

9. Find the mean, median, and range of the salaries given below. 



451 



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Table 11.6: 



Professional Realm Annual income 



Farming, Fishing, and Forestry $19,630 

Sales and Related $28,920 

Architecture and Engineering $56,330 

Healthcare Practitioners $49,930 

Legal $69,030 

Teaching & Education $39,130 

Construction $35,460 

Professional Baseball Player* $2,476,590 



(Source: Bureau of Labor Statistics, except (*) - The Baseball Players' Association (playbpa.com)). 
Find the mean, median, mode, and range of the following data sets. 

10. 11, 16, 9, 15, 5, 18 

11. 53, 32, 49, 24, 62 

12. 11, 9, 19, 9, 19, 9, 13, 11 

13. 3, 2, 6, 9, 0, 1, 6, 6, 3, 2, 3, 5 

14. 2, 17, 1, -3, 12, 8, 12, 16 

15. 11, 21, 6, 17, 9. 

16. 223, 121, 227, 433, 122, 193, 397, 276, 303, 199, 197, 265, 366, 401, 222 

Find the mean, median, and standard deviation of the following numbers. Which, of the mean and median, 
will give the best average? 

17. 15, 19, 15, 16, 11, 11, 18, 21, 165, 9, 11, 20, 16, 8, 17, 10, 12, 11, 16, 14 

18. 11, 12, 14, 14, 14, 14, 19 

19. 11, 12, 14, 16, 17, 17, 18 

20. 6, 7, 9, 10, 13 

21. 121, 122, 193, 197, 199, 222, 223, 227, 265, 276, 303, 366, 397, 401, 433 

22. If each score on an algebra test is increased by seven points, how would this affect the: 

(a) Mean? 

(b) Median? 

(c) Mode? 

(d) Range? 

(e) Standard deviation? 

23. If each score of a golfer was multiplied by two, how would this affect the: 

(a) Mean? 

(b) Median? 

(c) Mode? 

(d) Range? 

24. Henry has the following World History scores: 88, 76, 97, 84. What would Henry need to score on 
his fifth test to have an average of 86? 

25. Explain why it is not possible for Henry to have an average of 93 after his fifth score. 

26. The mean of nine numbers is 105. What is the sum of the numbers? 

27. A bowler has the following scores: 163, 187, 194, 188, 205, 196. Find the bowler's average. 

www.ckl2.org 452 



28. Golf scores for a nine-hole course for five different players were: 38, 45, 58, 38, 36. 

(a) Find the mean golf score. 

(b) Find the standard deviation to the nearest hundredth. 

(c) Does the mean represent the most accurate center of tendency? Explain. 

29. Ten house sales in Encinitas, California are shown in the table below. Find the mean, median, and 
standard deviation for the sale prices. Explain, using the data, why the median house price is 
most often used as a measure of the house prices in an area. 

Table 11.7: 



Address 



Sale Price 



Date Of Sale 



643 3RD ST 

911 CORNISH DR 

911 ARDEN DR 

715 S VULCAN AVE 

510 4TH ST 

415 ARDEN DR 

226 5TH ST 

710 3RD ST 

68 LA VETA AVE 

207 WEST D ST 



$1,137,000 

$879,000 

$950,000 

$875,000 

$1,499,000 

$875,000 

$4,000,000 

$975,000 

$796,793 

$2,100,000 



6/5/2007 

6/5/2007 

6/13/2007 

4/30/2007 

4/26/2007 

5/11/2007 

5/3/2007 

3/13/2007 

2/8/2007 

3/15/2007 



30. Determine which statistical measure (mean, median, or mode) would be most appropriate for the 
following. 

(a) The life expectancy of store-bought goldfish. 

(b) The age in years of the audience for a kids' TV program. 

(c) The weight of potato sacks that a store labels as "5-pound bag." 

31. James and John both own fields in which they plant cabbages. James plants cabbages by hand, while 
John uses a machine to carefully control the distance between the cabbages. The diameters of each 
grower's cabbages are measured, and the results are shown in the table. John claims his method of 
machine planting is better. James insists it is better to plant by hand. Use the data to provide a 
reason to justify both sides of the argument. 

Table 11.8: 



James 



John 



Mean Diameter (inches) 7.10 

Standard Deviation (inches) 2.75 



6.85 
0.60 



32. Two bus companies run services between Los Angeles and San Francisco. The mean journey times 
and standard deviation in those times are given below. If Samantha needs to travel between the 
cities, which company should she choose if: 

(a) She needs to catch a plane in San Francisco. 

(b) She travels weekly to visit friends who live in San Francisco and wishes to minimize the time 
she spends on a bus over the entire year. 



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Table 11.9: 



Inter-Cal Express Fast-dog Travel 



Mean Time (hours) 9.5 8.75 

Standard Deviation (hours) 0.25 2.5 

Mixed Review 

33. A square garden has dimensions of 20 yards by 20 yards. How much shorter is it to cut across the 
diagonal than to walk around two joining sides? 

34. Rewrite in standard form: y = hx - 5. 

35. Solve for m: -2 = ifxT7. 

36. A sail has a vertical length of 15 feet and a horizontal length of 8 feet. To the nearest foot, how long 
is the diagonal? 

37. Rationalize the denominator: —p. 

11.7 Stem-and-Leaf Plots and Histograms 

Understanding data is a very important mathematical ability. You must know how to use data and interpret 
the results to make informed decisions about politics, food, and income. This lesson will show two ways 
to graph data: 

• as a stem-and-leaf plot and 

• as a histogram 

A stem-and-leaf plot is an organization of numerical data into categories based on place value. The stem- 
and-leaf plot is a graph that is similar to a histogram but it displays more information. For a stem-and-leaf 
plot, each number will be divided into two parts using place value. 

The stem is the left-hand column and will contain the digits in the largest place. The right-hand column 
will be the leaf and it will contain the digits in the smallest place. 

Example: In a recent study of male students at a local high school, students were asked how much money 
they spend socially on Prom night. The following numbers represent the amount of dollars of a random 
selection of 40 male students. 



25 


60 


120 


64 


65 


28 


110 


60 


70 


34 


35 


70 


58 


100 


55 


95 


55 


95 


93 


50 


75 


35 


40 


75 


90 


40 


50 


80 


85 


50 


80 


47 


50 


80 


90 


42 


49 


84 


35 


70 



Represent this data in a stem-and-leaf plot. 

Solution: The stems will be arranged vertically in ascending order (smallest to largest) and each leaf will 
be written to the right of its stem horizontally in order from least to greatest. 



www.ckl2.org 454 



Table 11.10: 



Stem Leaf 



2 5, 8 

3 4, 5, 5, 5 

4 0, 0, 2, 7, 9 

5 0, 0, 0, 0, 5, 5, 

6 0, 0, 4, 5 

7 0, 0, 0, 5, 5 

8 0, 0, 0, 4, 5 

9 0, 0, 3, 5, 5 

10 

11 

12 



This stem- and- leaf plot can be interpreted very easily. By looking at stem 6, you see that 4 males spent 
60 'some dollars' on Prom night. By counting the number of leaves, you know that 40 males responded to 
the question concerning how much money they spent on prom night. The smallest and largest data values 
are known by looking and the first and last stem-and-leaf. The stem-and-leaf is a 'quick look' chart that 
can quickly provide information from the data. This also serves as an easy method for sorting numbers 
manually. 

Interpreting and Creating Histograms 

Suppose you took a survey of 20 algebra students, asking their number of siblings. You would probably get 
a variety of answers. Some students would have no siblings while others would have several. The results 
may look like this. 

1, 4, 2, 1, 0, 2, 1, 0, 1, 2, 1, 0, 0, 2, 2, 3, 1, 1, 3, 6 

We could organize this many ways. The first way might just be to create an ordered list, relisting all 
numbers in order, starting with the smallest. 

0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 4, 6 

Another way to list the results is in a table. 

Table 11.11: 

Number of Siblings Number of Matching Students 

4 

1 7 

2 5 

3 2 

4 1 

5 

6 1 



A table showing the number of times a particular category appears in a data set is a frequency distri- 
bution. 



455 www.ckl2.org 



You could also make a visual representation of the data by making categories for the number of siblings on 
the x-axis and stacking representations of each student above the category marker. We could use crosses, 
stick-men or even photographs of the students to show how many students are in each category. 




Number of siblings 



This graph is called a histogram. 

A histogram is a bar chart that describes a frequency distribution. 

The horizontal axis of the histogram is separated into equal intervals. The vertical bars represent how 
many items are in each interval. 




8 9 10 



age 



Example: Jim collected data at a local fair. The above histogram relates the number of children of 
particular ages who visited the face-painting booth. What can you conclude using this histogram? 

Solution: 

• You can find the sum of the heights of each bar to determine how many children visited the face 
painting booth. 

1 + 3 + 4 + 5 + 6 + 7 + 3 + 1 = 30 children 

• The tallest bar is at age seven. There were more seven-year olds than any other age group. 

• There is no bar at one or ten. This means zero ten-year-olds and zero one-year-olds had their faces 
painted. 

Example: Studies (and logic) show that the more homework you do the better your grade in a course. In 
a study conducted at a local school, students in grade 10 were asked to check off what box represented the 
average amount of time they spent on homework each night. The following results were recorded: table 
on wiki... http: //authors . ckl2.org/wiki/index.php/0rganizing_and_Displaying_Data_-_Basic 



www.ckl2.org 



456 



Table 11.12: 



Time Spent on Homework 

(Hours) 



Tally 



Frequency (# of students) 



[0 - 0.5) 
[0.5 - 1.0) 
[1.0-1.5) 
[1.5-2.0) 
[2.0 - 2.5) 
2.5+ 



12 

23 

34 

26 

5 





Convert this data into a histogram. 
Solution: 





r™i 










Tim 


*Spe 


-it Stu 


dying 












£ 


■H7" 
































55 














































1 
E 


































z 




































-10- 







5 


1 


! 

Time 


i 1 
[hr) 


5 


2 





2.5 







Creating Histograms Using a Graphing Calculator 

Drawing a histogram is quite similar to drawing a scatter plot. Instead of graphing two lists, L\ and L2, 
you will graph only one list, L\. 

Consider the following data: The following unordered data represents the ages of passengers on a train 
carriage. 

35, 42, 38, 57, 2, 24, 27, 36, 45, 60, 38, 40, 40, 44, 1, 44, 48, 84, 38, 20, 4, 

2, 48, 58, 3, 20, 6, 40, 22, 26, 17, 18, 40, 51, 62, 31, 27, 48, 35, 27, 37, 58, 21. 

Begin by entering the data into [LIST 1] of the [STAT] menu. 



L1 



IB 

2? 
3? 



LI 



L3 



L1(H3J=21 

Choose [2 nd ] and [Y =] to enter into the [STATPLOT] menu. 

457 



www.cki2.0rg 



Off 

*Q*~ H3H |^ 

XlistiLi 
Fre-=i: 1 



Press [WINDOW] and ensure that Xmin and Xmax allow for all data points to be shown. The Xscl 
value determines the bin width. 

WINDOW 
Xnin=0 
Xnax=10@ 
Xscl=10 
Vnin=0 
Vnax=12 
Vscl=l 
Xres=i 

Press [GRAPH] to display the histogram. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Stem-and-Leaf Plots (6:45) 




Figure 11.15: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/829 

CK-12 Basic Algebra: Histograms (6:08) 

1. What is the stem in a stem-and-leaf plot? What is a leaf 7 What is an advantage to using a stem- 
and-leaf plot? 

2. Describe a histogram. What is an advantage of using a histogram? 

3. For each of the following examples, describe why you would likely use a histogram. 



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458 




Figure 11.16: (Watch Youtube Video) 

http://www.ckl2.org/fiexbook/embed/view/831 

(a) Frequency of the favorite drinks for the first 100 people to enter the school dance 

(b) Frequency of the average time it takes the people in your class to finish a math assignment 

(c) Frequency of the average distance people park their cars away from the mall in order to walk a 
little more 

4. Prepare a histogram using the following scores from a recent science test. Offer four conclusions you 
can make about this histogram? Include mean, median, mode, range, etc. 

Table 11.13: 



Score (%) 



Tally 



Frequency 



50-60 
60-70 
70-80 
80-90 
90-100 



4 
6 
11 



5. A research firm has just developed a streak-free glass cleaner. The product is sold at a number of 
local chain stores and its sales are being closely monitored. At the end of one year, the sales of 
the product are released. The company is planning on starting up an advertisement campaign to 
promote th§gg:oduct. Theg4ata is found f0^he chart bejxgqr . 219 163 



87 


248 


137 


193 


144 


89 


175 


164 


118 


248 


159 


123 


220 


141 


122 


143 


250 


168 


100 


217 


165 


226 


138 


131 



(a) Display the sales of the product before the ad campaign in a stem-and-leaf plot. 

(b) How many chain stores were involved in selling the streak-free glass cleaner? 

(c) In stem 1, what does the number 11 represent? What does the number 8 represent? 

(d) What percentage of stores sold less than 175 bottles of streak- free glass cleaner? 



6. Using the following data, answer the questions that follow. Data: 607.4, 886.0, 822.2, 755.7, 900.6, 
770.9, 780.8, 760.1, 936.9, 962.9, 859.9, 848.3, 898.7, 670.9, 946.7, 817.8, 868.1, 887.1, 881.3, 744.6, 
984.9, 941.5, 851.8, 905.4, 810.6, 765.3, 881.9, 851.6, 815.7, 989.7, 723.4, 869.3, 951.0, 794.7, 807.6, 
841.3, 741.5, 822.2, 966.2, 950.1 

A. Create a stem-and-leaf plot. Round each data point to the nearest tens place. Use the hundreds 
digit as the stem and the tens place as the leaf. 

(a) What is the mean of the data? 

(b) What is the mode of the data? 

(c) What is the median of the data? A K n 

459 www.ckl2.org 

B. Make a frequency table for the data. Use a bin width of 50. 

C. Plot the data as a histogram with a bin width of: 

fa) 50 



77 


80 


82 


68 


65 


59 


61 


57 


50 


62 


61 


70 


69 


64 


67 


70 


62 


65 


65 


73 


76 


87 


80 


82 


83 


79 


79 


77 


80 


71 













In order for Lizzie to see how well she is doing, create a stem-and-leaf plot of her scores. 

It is your job to entertain your younger sibling every Saturday morning. You decide to take the 

youngster to the community pool to swim. Since swimming is a new thing to do, your little buddy 

isn't too sure about the water and is a bit scared of the new adventure. You decide to keep a record of 

the length of time he stays in the water each morning. You recorded the following times (in minutes): 

12, 13, 21, 27, 33, 34, 35, 37, 40, 40, 41. Create a stem-and-leaf plot to represent this data. List two 

conclusions you can make from this graph. 

The following stem-and-leaf plot shows data collected for the speed of 40 cars in a 35 mph limit zone 

in Culver City, California. 

(a) Find the mean, median, and mode speed. 

(b) Complete a frequency table, starting at 25 mph with a bin width of 5 mph. 

(c) Use the table to construct a histogram with the intervals from your frequency table. 



6 7 8 8 9 

001 11 22223345556677 

0211244568 9 

7 



9 9 9 



10. The following histogram displays the results of a larger-scale survey of the number of siblings. Use 
it to find: 



21- 




20" 



fr 14" 
| 12- 



p 



1 23456789 10 11 
number of siblings 



(a) The median of the data 

(b) The mean of the data 

(c) The mode of the data 

(d) The number of people who have an odd number of siblings 

(e) The percentage of the people surveyed who have four or more siblings 

11. Use the stem-and-leaf plot to devise a situation that follows the data. 
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6 

7 5 

8 8 2 

9 

12. An oil company claims that its premium- grade gasoline contains an additive that significantly in- 
creases gas mileage. To prove their claim, the company selected 15 drivers and first filled each of 
their cars with 45L of regular gasoline and asked them to record their mileage. The company then 
filled each of the cars with 45L of premium gasoline and again asked them to record their mileage. 
The results below show the number of kilometers each car traveled. 

Table 11.14: Regular Gasoline 



640 


570 


660 580 


610 


540 
550 


555 
590 


588 615 

585 587 


570 
591 


Table 11.15: Premium Gasoline 


659 


619 


639 629 


664 


635 

694 


709 
638 


637 633 

689 589 


618 
500 



Display each set of data to explain whether or not the claim made by the oil company is true or false. 
Mixed Review 

13. How many ways can a nine-person soccer team line up for a picture if the goalie is to be in the center? 

14. Graph 8x + 5y = 40 using its intercepts. 

15. Simplify (gg)" 2 . 

16. Rewrite in standard form: y = -3(x - l) 2 + 4. 

17. Graph f(x) = ^. 

18. A ball is dropped from a height of 10 meters. When will it reach the ground? 

hx + 4y = 9 

19. Solve the following system: < 

[9x+12y = 27 

11.8 Box-and- Whisker Plots 

A box-and-whisker plot is another type of graph used to display data. It shows how the data are 
dispersed around a median, but it does not show specific values in the data. It does not show a distribution 
in as much detail as does a stem-and-leaf plot or a histogram. 

A box-and-whisker plot is a graph based upon medians. It shows the minimum value, the lower median, 
the median, the upper median, and the maximum value of a data set. It is also known as a box plot. 

This type of graph is often used when the number of data values is large or when two or more data sets 
are being compared. 

461 www.ckl2.org 



Example: You have a summer job working at Paddy's Pond. Your job is to measure as many salmon as 
possible and record the results. Here are the lengths (in inches) of the first 15 fish you found: 13, 14, 6, 9, 
10, 21, 17, 15, 15, 7, 10, 13, 13, 8, 11 

Solution: Since the box-and-whisker plot is based on medians, the first step is to organize the data in order 
from smallest to largest. 



6, 7, 8, 9, 10, 10, 11, 13 , 13, 13, 14, 15, 15, 17, 21 



Step 1: Find the median: median = 13. 

Step 2: Find the lower median. 

The lower median is the median of the lower half of the data. It is also called the lower quartile or Q\. 



6, 7, 8, 9 , 10, 10, 11 



2i = 9 

Step 3: Find the upper median. 

The upper median is the median of the upper half of the data. It is also called the upper quartile or (?2- 



13, 13, 14, 15 , 15, 17, 21 



03 = 15 

Step 4: Draw the box plot. The numbers needed to construct a box-and-whisker plot are called the 
five-number summary. 

The five- number summary are: the minimum value, <2i, the median, (?2, and the maximum value. 
Minimum = 6; Q\ = 9; median = 13; Qs = 15; maximum = 21 






1 2 3 4 5 6 7 S 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 23 29 3G 

The three medians divide the data into four equal parts. In other words: 

• One-quarter of the data values are located between 6 and 9. 

• One-quarter of the data values are located between 9 and 13. 

• One-quarter of the data values are located between 13 and 15. 

• One-quarter of the data values are located between 15 and 21. 

From its whiskers, any outliers (unusual data values that can be either low or high) can be easily seen on 
a box-and-whisker plot. An outlier would create a whisker that would be very long. 



Whisker 



Box 



Whisker 



Smallest Number 

"--I 




Largest Number 



Median of Lower Quartile 9 



Median of Upper Quartile 15 



3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 3G 



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462 



Each whisker contains 25% of the data and the remaining 50% of the data is contained within the box. It 
is easy to see the range of the values as well as how these values are distributed around the middle value. 
The smaller the box, the more consistent the data values are with the median of the data. 

Example: After one month of growing, the heights of 24 parsley seed plants were measured and recorded. 
The measurements (in inches) are given here: 6, 22, 11, 25, 16, 26, 28, 37, 37, 38, 33, 40, 34, 39, 23, 11, 

48, 49, 8, 26, 18, 17, 27, 14. 

Construct a box-and-whisker plot to represent the data. 

Solution: To begin, organize your data in ascending order. There is an even number of data values so the 
median will be the mean of the two middle values. Med = — ^ — = 26. The median of the lower quartile 
is the number in the number between the 6th and 7th position, which is the average of 16 and 17, or 16.5. 
The median of the upper quartile is also the number between the 6th and 7th position, which is the average 
of 37 and 37, or 37. The smallest number is 6 and the largest number is 49. 

Height of Parsley Seedlings 



6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 



Creating Box-and- Whisker Plots Using a Graphing Calculator 

The TI83 can also be used to create a box-and-whisker plot. The five- number summary values can be 
determined by using the trace function of the calculator. 

Enter the data into [Li]. 



L1 


LI 


L3 1 


B 

11 

11 

12 

IH 

lb 







Change the [STATPLOT] to a box plot instead of a histogram. 

Off 

rype: Lil L± Jhn 
m*- 3»e i.-" 

XlistiLi 
Fre*i: 1 



Lotl...0n 
> ohli i 

2:Plot2...0ff 

L±L3 LH 

3:Plot3...0ff 

!■■■■• L1 LE 

4+PlotsOff 



463 



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Box-and- whisker plots are useful when comparing multiple sets of data. The graphs are plotted, one above 
the other, to visualize the median comparisons. 

Example: Using the data from the previous lesson, determine whether the additive improved the gas 
mileage. 

Table 11.16: Regular Gasoline 



540 


550 


555 


570 


570 


580 
591 


585 
610 


587 
615 


588 
640 


590 
660 



Solution: 



Table 11.17: Premium Gasoline 



500 


589 


618 


619 


629 


633 
659 


635 
664 


637 

689 


638 
694 


639 
709 



Table 11.18: Five-Number Summary 



Regular Gasoline 



Premium Gasoline 



Smallest # 

Qi 

Median 
Largest # 



540 
570 
587 
610 
660 



500 
619 
637 
664 
709 



Regular Gasoline 
vs. Premium 
Gasoline 



J T 



490 510 530 550 570 590 610 630 650 670 690 710 

From the above box-and- whisker plots, where the blue one represents the regular gasoline and the yellow 



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464 



one the premium gasoline, it is safe to say that the additive in the premium gasoline definitely increases 
the mileage. However, the value of 500 seems to be an outlier. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Box-and- Whisker Plots (13:14) 




Figure 11.17: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/832 



1. Describe the five- number summary. 

2. What is the purpose of a box- and- whisker plot? When it is useful? 

3. What are some disadvantages to representing data with a box- and- whisker plot? 

4. Following is the data that represents the amount of money that males spent on Prom night. 

25 60 120 64 65 28 110 60 



70 



34 



35 



70 



58 



100 



55 



95 



55 


95 


93 


50 


75 


35 


40 


75 


90 


40 


50 


80 


85 


50 


80 


47 


50 


80 


90 


42 


49 


84 


35 


70 



Construct a box-and-whisker graph to represent the data. 
5. Forty students took a college algebra entrance test and the results are summarized in the box-and- 
whisker plot below. How many students would be allowed to enroll in the class if the pass mark was 
set at: 

(a) 65 % 

(b) 60 % 



Percent score 

— * 



40 50 60 70 80 90 100 

6. Harika is rolling three dice and adding the scores together. She records the total score for 50 rolls, 
and the scores she gets are shown below. Display the data in a box-and-whisker plot, and find both 
the range and the inter-quartile range. 9, 10, 12, 13, 10, 14, 8, 10, 12, 6, 8, 11, 12, 12, 9, 11, 10, 15, 
10, 8, 8, 12, 10, 14, 10, 9, 7, 5, 11, 15, 8, 9, 17, 12, 12, 13, 7, 14, 6, 17, 11, 15, 10, 13, 9, 7, 12, 13, 10, 
12 



465 



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7. The box-and- whisker plots below represent the times taken by a school class to complete a 150-yard 
obstacle course. The times have been separated into boys and girls. The boys and the girls both 
think that they did best. Determine the five-number summary for both the boys and the girls and 
give a convincing argument for each of them. 



h 



hzz: 



-cm 



Girls 



Boys 



12 3 4 5 time in minutes 

8. Draw a box-and-whisker plot for the following unordered data. 49, 57, 53, 54, 49, 67, 51, 57, 56, 59, 
57, 50, 49, 52, 53, 50, 58 

9. A simulation of a large number of runs of rolling three dice and adding the numbers results in the 
following five-number summary: 3, 8, 10.5, 13, 18. Make a box-and-whisker plot for the data. 

10. The box-and-whisker plots below represent the percentage of people living below the poverty line 
by county in both Texas and California. Determine the five-number summary for each state, and 
comment on the spread of each distribution. 



11. 



HZf 



-| California 



Texas 



5 10 15 20 25 30 35 % in poverty 

The five-number summary for the average daily temperature in Atlantic City, NJ (given in Fahren- 
heit) is 31, 39, 52, 68, 76. Draw the box-and-whisker plot for this data and use it to determine which 
of the following would be considered an outlier if it were included in the data. 



(a) January's record-high temperature of 78° 

(b) January's record-low temperature of -8° 

(c) April's record-high temperature of 94° 

(d) The all-time record high of 106° 



12. In 1887, Albert Michelson and Edward Morley conducted an experiment to determine the speed of 
light. The data for the first ten runs (five results in each run) is given below. Each value represents 
how many kilometers per second over 299,000 km/ sec was measured. Create a box-and-whisker plot 
of the data. Be sure to identify outliers and plot them as such.900, 840, 880, 880, 800, 860, 720, 720, 
620, 860, 970, 950, 890, 810, 810, 820, 800, 770, 850, 740, 900, 1070, 930, 850, 950, 980, 980, 880, 
960, 940, 960, 940, 880, 800, 850, 880, 760, 740, 750, 760, 890, 840, 780, 810, 760, 810, 790, 810, 820, 
850 

13. Using the following box-and-whisker plot, list three pieces of information you can determine from the 
graph. 



75 100 125 150 175 200 225 

14. In a recent survey done at a high school cafeteria, a random selection of males and females were 
asked how much money they spent each month on school lunches. The following box-and-whisker 
plots compare the responses of males to those of females. The lower one is the response by males. 



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466 



M U I H H I H H I I t I + I H M 1 M H I I I I H H H I H ti ( I M I I 
10 20 30 40 50 60 70 80 90 10C 



(a) How much money did the middle 50% of each gender spend on school lunches each month? 

(b) What is the significance of the value $42 for females and $46 for males? 

(c) What conclusions can be drawn from the above plots? Explain. 

15. Multiple Choice. The following box- and- whisker plot shows final grades last semester. How would 
you best describe a typical grade in that course? 



34 41 58 62 

A. Students typically made between 82 and 88. 

B. Students typically made between 41 and 82. 

C. Students typically made around 62. 

D. Students typically made between 58 and 82. 



82 



88 



Mixed Review 

16. Find the mean, median, mode, and range for the following salaries in an office building: 63,450; 
45,502; 63,450; 5 1,769; 63,450; 35,120; 45,502; 63,450; 31,100; 42,216; 49,108; 63,450; 37,904 

17. Graph g(x) = 2 V* 3 ! - 3. 

18. Translate into an algebraic sentence: The square root of a number plus six is less than 18. 

19. Solve for y: 6(v - 11) + 9 = |(27 + 3y) - 16. 

20. A fundraiser is selling two types of items: pizzas and cookie dough. The club earns $5 for each pizza 
sold and $4 for each container of cookie dough. They want to earn more than $550. 

(a) Write this situation as an inequality. 

(b) Give four combinations that will make this sentence true. 

21. Find the equation for a line parallel to x + 2y = 10 containing the point (2, 1). 

11.9 Chapter 11 Review 

Explain the shift of each function from the parent function f(x) = ^fx. 

1. /(*)= V^ + 7 

2. f(x) = V*+~3 
3- g{x) = -V* 

4. y = 3 + Vx-1 

Graph the following square root functions. Identify the domain and range of each. 



5. f{x) 

6. g(x) 
7- /(*) 



Vx - 2 + 5 
-Vx+1 
V2^-2 



467 



www.ckl2.org 



Simplify the following, if possible. Write your answer in its simplest form. 

8 - V? X V 27 

9. V5- V7 

10. vrix vn 

11. ^p 

V2 

12. 8Vi+llV4 

13. 5V80-12V5 

14. VI0+ V2 

15. V2I- V6 

16. V27+ V81 

17. 4V3-2V6 

18. V3x Vf 

19. 6V72 

20. rV(§) 

22. ^ 



V5 



23 - t 

24. 8VI0-3V40 

25. V27+ V3 

Solve each equation. If the answer is extraneous, say so. 

26. 8 = V2l 

27. x = V7x 

28. V2 + 2m = V4-m 

29. V35 - 2x = -1 

30. 14 = 6 + V10 - 6x 

31.4+^f = 5 

32. V-9 - 2x = V-l-x 

33. -2 = -^6 

34. 5 Vl0^6 V^ 

35. Vx 2 + 3x = 2 

36. V? = 5 

37. A leg of a right triangle is 11. Its hypotenuse is 32. What is the length of the other leg? 

38. Can 9, 12, 15 be sides of a right triangle? 

39. Two legs of a right triangle have lengths of 16 and 24. What is the length of the hypotenuse? 

40. Can 20, 21, and 29 be the sides of a right triangle? 

Find the distance between the two points. Then find the midpoint. 

41. (0, 2) and (-5, 4) 

42. (7, -3) and (4, -3) 

43. (4, 6) and (-3, 0) 

44. (8, -3) and (-7, -6) 

45. (-8, -7) and (6, 5) 

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46. (-6, 6) and (0, 8) 

47. (2, 6) is six units away from a second point. Find the two possibilities for this ordered pair. 

48. (9, 0) is five units away from a second point. Find the two possibilities for this ordered pair. 

49. The midpoint of a segment is (7.5, 1.5). Point A is (-5, -6). Find the other endpoint of the segment. 

50. Maggie started at the center of town and drove nine miles west and five miles north. From this 
location, she drove 16 miles east and 12 miles south. What is the distance from this position from 
the center of town? What is the midpoint? 

51. The surface area of a cube is given by the formula S A = 6s 2 . The surface area is 337.50 square 
inches. What is the side length of the cube? 

52. The diagonal of a sail is 24 feet long. The vertical length is 16 feet. If the area is found by 
\ (length) (height) , determine the area of the sail. 

53. A student earned the following test scores: 63, 65, 80, 84, 73. What would the next test score have 
to be in order to have an average of 70? 

54. Find the mean, median, mode, and range of the data set. 11, 12, 11, 11, 11, 13, 13, 12, 12, 11, 12, 
13, 13, 12, 13, 11, 12, 12, 13 

55. A study shows the average teacher earns $45,000 annually. Most teachers do not earn close to this 
amount. 

(a) Which central tendency was most likely used to describe this situation? 

(b) Which measure of central tendency should be used to describe this situation? 

56. Mrs. Kramer's Algebra I class took a test on factoring. She recorded the scores as follows: 55, 57, 
62, 64, 66, 68, 68, 68, 69, 72, 75, 77, 78, 79, 79, 82, 83, 85, 88, 90, 90, 90, 90, 92, 94, 95, 97, 99 

(a) Construct a histogram using intervals of ten, starting with 50-59. 

(b) What is the mode? What can you conclude from this graph? 

57. Ten waitresses counted their tip money and collected the following data: $32, $58, $17, $27, $69, 
$73, $42, $38, $24, and $52. Display this information in a stem- and-leaf plot. 

58. Eleven people were asked how many miles they live from their place of work. Their responses are: 
5.2, 18.7, 8.7, 9.1, 2.3, 2.3, 5.4, 22.8, 15.2, 7.8, 9.9. Display this data as a box-and-whisker plot. 

59. What is one disadvantage to a box-and-whisker plot? 

60. Fifteen students were randomly selected and asked, "How many times have you checked Facebook 
today?" Their responses are: 4, 23, 62, 15, 18, 11, 13, 2, 8, 7, 12, 9, 14, 12, 20. Display this 
information as a box-and-whisker plot and interpret its results. 

61. What effect does an outlier have on the look of a box-and-whisker plot? 

62. Multiple Choice. The median always represents which of the following?A. The upper quartile 

B. The lower quartile 

C. The mean of the data 

D. The 50% percentile 



11.10 Chapter 11 Test 



1. Describe each type of visual display presented in this chapter. State one advantage and one disad- 
vantage for each type of visual display. 

2. Graph f(x) = 7 + yjx — 4. State its domain and range. What is the ordered pair of the origin? 

3. True or false? The upper quartile is the mean of the upper half of the data. 

4. What is the domain restriction of y = ifx? 

5. Solve -6 = 2^T5. 

6. Simplify ^. 

7. Simplify and reduce: V3x V81. 

469 www.ckl2.org 



8. A square baking dish is 8 inches by 8 inches. What is the length of the diagonal? What is the area 
of a piece cut from corner to opposite corner? 

9. The following data consists of the weights, in pounds, of 24 high school students: 195, 206, 100, 98, 
150, 210, 195, 106, 195, 108, 180, 212, 104, 195, 100, 216, 99, 206, 116, 142, 100, 135, 98, 160. 

(a) Display this information in a box plot, a stem-and-leaf plot, and a histogram with a bin width 
of 10. 

(b) Which graph seems to be the best method to display this data? 

(c) Are there any outliers? 

(d) List three conclusions you can make about this data. 

10. Find the distance between (5, -9) and (-6, -2). 

11. The coordinates of Portland, Oregon are (43.665, 70.269). The coordinates of Miami, Florida are 

(25.79, 80.224). 

(a) Find the distance between these two cities. 

(b) What are the coordinates of the town that represents the halfway mark? 

12. The Beaufort Wind Scale is used by coastal observers to estimate the wind speed. It is given by the 
formula s 2 = 3.5Z? 3 , where s = the wind speed (in knots) and B = the Beaufort value. 

(a) Find the Beaufort value for a 26-knot wind. 

(b) What is the wind speed of a severe storm with a gale wind of 50 knots? 

13. Find the two possibilities for a coordinate ten units away from (2, 2). 

14. Use the following data obtained from the American Veterinary Medical Association. It states the 
number of households per 1,000 with particular exotic animals. 

15. (a) Find the mean, median, mode, range, and standard deviation. 

(b) Are there any outliers? What effect does this have on the mean and range? 

Table 11.19: 

Households 

(in 1,000) 

Fish 9,036 

Ferrets 505 

Rabbits 1,870 

Hamsters 826 

Guinea Pigs 628 

Gerbils 187 

Other Rodents 452 

Turtles 1,106 

Snakes 390 

Lizards 719 

http : //www . avma . org/ref erence/marketstat s/def ault . asp 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. or g/flexr/ chapter/ 9 621. 



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Chapter 12 

Rational Equations and 
Functions; Statistics 



The final chapter of this text introduces the concept of rational functions, that is, equations in which the 
variable appears in the denominator of a fraction. A common rational function in the inverse variation 
model, similar to the direct variation model you studied in chapter 4 lesson 6. We finish the chapter with 
solving rational equations and using graphical representations to display data. 

12.1 Inverse Variation Models 

In Chapter 4, Lesson 6, you learned how to write direct variation models. In direct variation, the variables 
changed in the same way and the graph contained the origin. But what happens when the variables change 
in different ways? Consider the following situation. 

A group of friends rent a beach house and decide to split the cost of the rent and food. Four friends pay 
$170 each. Five friends pay $162 each. Six friends pay $157. If nine people were to share the expense, how 
much would each pay? 

Let's look at this in a table. 

Table 12.1: 

n (number of friends) t (share of expense) 

4 170 

5 162 

6 157 
9 ??? 

As the number of friends gets larger, the cost per person gets smaller. This is an example of inverse 
variation. 

An inverse variation function has the form f(x) = -, where k is called the constant of variation and 
must be a counting number and x ^ 0. 

To show an inverse variation relationship, use either of the phrases: 
• Is inversely proportional to 

471 www.ckl2.org 



• Varies inversely as 

Example 1: Find the constant of variation of the beach house situation. 
Solution: Use the inverse variation equation to find k, the constant of variation. 

k 



y = 


X 




170 = 


k 

I 




170 x 4 = 


k 
4 X 


4 



Solve for k : 

fc = 680 

You can use this information to determine the amount of expense per person if nine people split the cost. 

_ 680 

x 

680 
y = — = 75.56 

If nine people split the expense, each would pay $75.56. 
Using a graphing calculator, look at a graph of this situation. 

WINDOW 
Xnin=-10 
Xnax=10 
Xscl=l 
Vnin="700 
Vnax=700 
Vscl=50 
Xres=i 



The graph of an inverse variation function f(x) = - is a hyperbola. It has two branches in opposite 
quadrants. 

If k > 0, the branches are in quadrants I and III. 

If k < 0, the branches are in quadrants II and IV. 

The graph appears to not cross the axes. In fact, this is true of any inverse variation equation of the form 
y = Jr. These lines are called asymptotes. Because of this, an inverse variation function has a special 
domain and range. 

Domain : x £ 
Range : y ± 

You will investigate these excluded values in later lessons of this chapter. 
www.ckl2.org 472 



Example 2: The frequency, /, of sound varies inversely with wavelength, A. A sound signal that has a 
wavelength of 34 meters has a frequency of 10 hertz. What frequency does a sound signal of 120 meters 
have? 

Solution: Use the inverse variation equation to find k, the constant of variation. 

k 



f = 



10 



Solve for k 



Use k to answer the question: 



A 

k 

34 
k 



10 x 34 = — x 34 

34 

k = 340 



340 
f = 120 = 2 * 83 hem 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Proportionality (17:03) 




Figure 12.1: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/833 



1. Define inverse variation. 

2. Using 4.6 as a reference, explain three main differences between direct variation and inverse variation. 

Read each statement and decide if the relationship is direct, inverse, or neither. 



3. The weight of a book as the number of pages it contains. 

4. The temperature outside as the time of day. 

5. The amount of prize money you receive from winning the lottery as the number of 

people who split the ticket cost. 

6. The cost of a ferry ride 

7. The area of a square 



8. The height from the ground 
been on a roller coaster. 



as the number of times you ride. 

as the length of its side. 

as the number of seconds you have 



473 



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9. The time it takes to wash a car as the number of people helping. 

10. The number of tiles it takes to tile a floor as the size of each tile. 

Graph each inverse equation. State the domain and range. 



11. 






12. 


y = i? 




13. 


/(*) = 


_4 

X 


14. 


J X 




15. 


h{x) = ■ 


_1 

X 


16. 


y = h 




17. 


8(x) = ■ 


2 

X 2 


18. 


y = ^ 




19. 


y = h 





In 20-25, model each situation with an inverse variation equation, finding k. Then answer the question. 

20. y varies inversely as x. If y = 24 when x = 3, find y when x = -1.5. 

21. d varies inversely as the cube of t. If d = -23.5 when t = 3, find d when x = \. 

22. If z is inversely proportional to w and z = 81 when w = 9, find w when z = 24. 

23. If v is inversely proportional to x and y = 2 when jc = 8, find y when x = 12. 

24. If a is inversely proportional to the square root of /?, and a = 32 when Z? = 9, find b when a = 6. 

25. If w is inversely proportional to the square of u and w = 4 when w = 2, find w when w = 8. 

26. The law of the fulcrum states the distance from the fulcrum varies inversely as the weight of the 
object. Joey and Josh are on a seesaw. If Joey weighs 40 pounds and sits six feet from the fulcrum, 
how far would Josh have to sit to balance the seesaw? (Josh weighs 65 pounds.) 

27. The intensity of light is inversely proportional to the square of the distance between the light source 
and the object being illuminated. A light meter that is 10 meters from a light source registers 35 
lux. What intensity would it register 25 meters from the light source? 

28. Ohm's Law states that current flowing in a wire is inversely proportional to the resistance of the wire. 
If the current is 2.5 amperes when the resistance is 20 ohms, find the resistance when the current is 
5 amperes. 

29. The number of tiles it takes to tile a bathroom floor varies inversely as the square of the side of the 
tile. If it takes 112 six-inch tiles to cover a floor, how many eight-inches tiles are needed? 

Mixed Review 

30. Solve and graph the solutions on a number line: 16 > -3x + 5. 

31. Graph on a coordinate plane: x = jg. 

32. Simplify ^320. 

33. State the Commutative Property of Multiplication. 

34. Draw the real number hierarchy and provide an example for each category. 

35. Find 17.5% of 96. 

12.2 Graphs of Rational Functions 

In the previous lesson, you learned the basics of graphing an inverse variation function. The hyperbola 
forms two branches in opposite quadrants. The axes are asymptotes to the graph. This lesson will 
compare graphs of inverse variation functions. You will also learn how to graph other rational equations. 

www.ckl2.org 474 



Example: Graph the function f{x) = | for the following values of k: 

* = -2,-l,--,l,2,4 

Each graph is shown separately then on one coordinate plane. 

As mentioned in the previous lesson, if k is positive, then the branches of the hyperbola are located in 
quadrants I and III. If k is negative, the branches are located in quadrants II and IV. Also notice how the 
hyperbola changes as k gets larger. 

Rational Functions 

A rational function is a ratio of two polynomials (a polynomial divided by another polynomial). The 
formal definition is: 

f(x) = —-—, where h(x) ± 

An asymptote is a value for which the equation or function is undefined. Asymptotes can be vertical, 
horizontal, or oblique. This text will focus on vertical asymptotes; other math courses will also show you 
how to find horizontal and oblique asymptotes. A function is undefined when the denominator of a fraction 
is zero. To find the asymptotes, find where the denominator of the rational function is zero. These are 
called points of discontinuity of the function. 

The formal definition for asymptote is as follows. 

An asymptote is a straight line to which, as the distance from the origin gets larger, a curve gets closer 
and closer but never intersects. 

Example: Find the points of discontinuity and the asymptote for the function y = ^g. 

Solution: Find the value of x for which the denominator of the rational function is zero. 

= x-5— >x=5 

The point at which x = 5 is a point of discontinuity. Therefore, the asymptote has the equation x = 5. 

Look at the graph of the function. There is a clear separation of the branches at the vertical line five units 
to the right of the origin. 



LI I I I I I I 



I I I I I I I I I I 



The domain is "all real numbers except five" or symbolically written x + 5. 

Example 1: Determine the asymptotes of t(x) = , _ 2 w 3 x . 

Solution: Using the Zero Product Property, there are two cases for asymptotes, where each set of paren- 
theses equals zero. 

475 www.ckl2.org 



x-2 = 
;t + 3 = 



x = 2 

x = -3 



The two asymptotes for this function are x = 2 and x = -3. 

Check your solution by graphing the function. 

The domain of the rational function above has two points of discontinuity. Therefore, its domain cannot 
include the numbers 2 or -3. The domain: x £ 2,x ± -3. 



Horizontal Asymptotes 

Rational functions can also have horizontal asymptotes. The equation of a horizontal asymptote is y = c, 
where c represents the vertical shift of the rational function. 

Example: Identify the vertical and horizontal asymptotes of f(x) = ( 4 w +8 \ 

Solution: The vertical asymptotes occur where the denominator is equal to zero. 

x -4 = -> x = 4 
x + 8 = 0->x = -8 



5. 



The vertical asymptotes are x = 4 and x = -8. 

The rational function has been shifted down five units fix) = - ( 

Therefore, the horizontal asymptote is y = -5. 



(x-4)(x+8) 



5. 



Multimedia Link: For further explanation about asymptotes, read through this PowerPoint presentation 
presented by North Virginia Community College or watch this CK-12 Basic Algebra: Finding Vertical 
Asymptotes of Rational Functions - YouTube video. 




Figure 12.2: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/834 



Real- World Rational Functions 

Electrical circuits are commonplace is everyday life. For instance, they are present in all electrical appliances 
in your home. The figure below shows an example of a simple electrical circuit. It consists of a battery 
that provides a voltage (V, measured in Volts), a resistor (7?, measured in ohms, ft) that resists the flow 
of electricity, and an ammeter that measures the current (/, measured in amperes, A) in the circuit. Your 
light bulb, toaster, and hairdryer are all basically simple resistors. In addition, resistors are used in an 



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476 



electrical circuit to control the amount of current flowing through a circuit and to regulate voltage levels. 
One important reason to do this is to prevent sensitive electrical components from burning out due to too 
much current or too high a voltage level. Resistors can be arranged in series or in parallel. 

For resistors placed in a series, the total resistance is just the sum of the resistances of the individual 
resistors. 

Rtot = R\-\- R2 
— Wy — W* — 

Rl R2 

For resistors placed in parallel, the reciprocal of the total resistance is the sum of the reciprocals of the 
resistances of the individual resistors. 

11 1 
Re Ri R2 

Rl 






R2 
Ohm's Law gives a relationship between current, voltage, and resistance. It states that: 

R 



V 




Example: Find the value of x marked in the diagram. 



12 V -=• 




X 



Solution: Using Ohm's Law, / = j£, and substituting the appropriate information yields: 



2 = 1? 

R 



Using the cross multiplication of a proportion yields: 

2R = 12 -» R = 6 ft 

477 



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Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Asymptotes (21:06) 




Figure 12.3: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/835 

CK-12 Basic Algebra: Another Rational Function Graph Example (8:20) 




Figure 12.4: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/836 

CK-12 Basic Algebra: A Third Example of Graphing a Rational Function (11:31) 




Figure 12.5: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/837 



1. What is a rational function? 

2. Define asymptote. How does an asymptote relate algebraically to an rational equation? 

3. Which asymptotes are described in this lesson? What is the general equation for these asymptotes? 



Identify the vertical and horizontal asymptotes of each rational function. 
www.ckl2.org 478 



4 v= — 

*• y x+2 

5. f{x) 



10 



2x-6 



+ 3 



6. y 

7.g(x) = ^-2 

8- h(x) = ^ 

9 - y = x 2 +4x+3 + 2 

l0.y=A" 8 

11. f{x) = 3 



x 2 -2x-8 



Graph each rational function. Show the vertical asymptote and horizontal asymptote as a dotted line. 



12 - y = -- x 

14- /(*) = J 

15- *(*) = ^ + 5 
16^=^2-6 
17- fix) = ^ 

18. ft(jc) = 4 

19. y 

20. j(x) = 3^ + 1 

22- /(*) = ^ 

23- *(*) = ^rfri 

24- *(*) = ^6 - 2 



-2 

X 2 + l 



x 2 +9 



Find the quantity labeled x in the following circuit. 




27. 



1.2 A 



X 



I5V ■=■ I0Q g 5 I5fl 

I 



479 



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Mixed Review 

28. A building 350 feet tall casts a shadow \mile long. How long is the shadow of a person five feet tall? 

29. State the Cross Product Property. 

30. Find the slope between (1, 1) and (-4, 5). 

31. The amount of refund from soda cans in Michigan is directly proportional to the number of returned 
cans. If you earn $12.00 refund for 120 cans, how much do you get per can? 

32. You put the letters from VACATION into a hat. If you reach in randomly, what is the probability 
you will pick the letter A? 

33. Give an example of a sixth-degree binomial. 

12.3 Division of Polynomials 

We will begin with a property that is the converse of the Adding Fractions Property presented in Chapter 
2. 

For all real numbers a,/?, and c, and c ± 0, ^- = ~ c + ~ c . 

This property allows you to separate the numerator into its individual fractions. This property is used 
when dividing a polynomial by a monomial. 

Example: Simplify 8x2 "^ +16 

Solution: Using the property above, separate the polynomial into its individual fractions. 

8x 2 4x 16 
Reduce. 4jc 2 - 2x + 8 



Example 1: Simplify " 3m2 ^ 8m+6 . 

Solution: Separate the trinomial into its individual fractions and reduce. 

3m 2 18m 6 

9m 9m 9m 

m 2 

2 + — 

3 3m 

Polynomials can also be divided by binomials. However, instead of separating into its individual fractions, 
we use a process called long division. 

Example: Simplify * 2 +^ +5 . 

Solution: When we perform division, the expression in the numerator is called the dividend and the 
expression in the denominator is called the divisor. 

To start the division we rewrite the problem in the following form. 



x + sY 



x 2 + 4x + 5 



Start by dividing the first term in the dividend by the first term in the divisor — = x. Place the answer 
on the line above the x term. 

www.ckl2.org 480 



x + 3j 



x 



x 2 + 4x + 5 



Next, multiply the x term in the answer by each of the x-\-3 terms in the divisor and place the result under 
the divided, matching like terms. 

multiply/^ " x 

x + 3 J x 2 + 4x ■ + 5 

x (x + 3K* x 2 + 3x 

Now subtract x 2 + 3x from x 2 + 4x + 5. It is useful to change the signs of the terms of x 2 + 3x to -x 2 - 3x 
and add like terms vertically. 



x + 3) x* + 4x + 5 



-x'-Sx 



Now, bring down 5, the next term in the dividend. 



x + 3) x 2 + 4x + 5 



x + 5 

Repeat the process. First divide the first term of x + 5 by the first term of the divisor (|) = 1. Place this 
answer on the line above the constant term of the dividend. 

X+ 1 



x + 3) x 3 + 4x + 5 

-x*-3x 

x + 5 

Multiply 1 by the divisor x + 3 and write the answer below x + 5, matching like terms. 
multiply 

x + 3 J x 2 + 4x + 5 



x+ 1 



x 2 -3x 




481 



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Subtract x + 3 from x + 5 by changing the signs of x + 3 to -x - 3 and adding like terms. 

x + 1 quotient 

x + 3) x 2 + 4x+ 5 



x + 5 

-x-3 

2 remainder 

Since there are no more terms from the dividend to bring down, we are done. 

The answer is x + 1 with a remainder of 2. 

Multimedia Link: For more help with using long division to simplify rational expressions, visit this 
http://www.purplemath.com/modules/polydiv2.htm - website or watch this CK-12 Basic Algebra: 6 7 
Polynomial long division with Mr. Nystrom - YouTube video. 




Figure 12.6: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/838 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. CK-12 Basic Algebra: Polynomial Division (12:09) 




Figure 12.7: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/839 



Divide the following polynomials. 



1. 



2x+4 



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482 



2. ill 



3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 



jc-4 
5.X-35 



5x 

x 2 +2jc-5 

4x 2 + 12jc-36 

-4jc 
2x 2 + 10x+7 

2x 2 
x 3 -x 
-2x 2 
5x 4 -9 

3x 
x 3 -12x 2 +3x-4 

12x 2 
3-6x+x 3 

-9x 3 
x 2 +3x+6 

x+1 
x 2 -9x+6 

x-1 
x 2 +5x+4 

x+4 
x 2 -10x+25 

x— 5 
x 2 -20x+12 

x-3 
3x 2 -x+5 

x-2 
9x 2 +2x-8 

x+4 
3x 2 -4 
3x+l 
5x 2 +2x-9 

2x-l 
x 2 -6x-12 

5x+4 
x 4 -2x 
8x+24 
x 3 +l 



4x-l 

Mixed Review 

23. Boyle's Law states that the pressure of a compressed gas varies inversely as its volume. If the pressure 
of a 200-pound gas is 16.75 psi, find the pressure if the amount of gas is 60 pounds. 

24. Is 5x 3 + x 2 - x~ l + 8 an example of a polynomial? Explain your answer. 

25. Find the slope of the line perpendicular to y = -|jc + 5. 

26. How many two-person teams can be made from a group of nine individuals? 

27. What is a problem with face-to-face interviews? What do you think is a potential solution to this 
problem? 

28. Solve form: -4= ^p. 



12.4 Rational Expressions 



You have gained experience working with rational functions so far this chapter. In this lesson, you will 
continue simplifying rational expressions by factoring. 

To simplify a rational expression means to reduce the fraction into its lowest terms. 

To do this, you will need to remember a property about multiplication. 

For all real values a,b, and b ^ 0, y = a. 

Example: Simplify 2 J^ x 2 _ r 

Solution: 

Both the numerator and denominator can be factored using methods learned in Chapter 9. 

483 www.ckl2.org 



4* -2 2(2* -1) 

2x 2 + x - 1 ^ (2jc-1)(jc+1) 

The expression (2x - 1) appears in both the numerator and denominator and can be canceled. The 
expression becomes: 

4x-2 2 



2x 2 + x - 1 jc + 1 

Example 1: Simplify - g^-s" 1 • 

Solution: Factor both pieces of the rational expression and reduce. 

x 2 - 2jc + 1 (x-l)(x-l) 

8x-8 > 8(jc-1) 

jc 2 -2jc+1_jc-1 

8x-8 " 8 

Finding Excluded Values of Rational Expressions 

As stated in Lesson 2 of this chapter, excluded values are also called points of discontinuity. These are 
the values that make the denominator equal to zero and are not part of the domain. 

Example 2: Find the excluded values of 2*~^_ 6 • 

Solution: Factor the denominator of the rational expression. 

2x + 1 2x + 1 



x 2 -x-6 (jc + 2)(jc-3) 
Find the value that makes each factor equal zero. 

x = -2,x = 3 

These are excluded values of the domain of the rational expression. 

Real-Life Rational Expressions 

The gravitational force between two objects in given by the formula F = Tjr! 2 • The gravitation constant 
is given by G = 6.67 X 10~ n (N • m 2 /kg 2 ). The force of attraction between the Earth and the Moon is 
F = 2.0 x 10 20 N (with masses of rrn = 5.97 x 10 24 kg for the Earth and m 2 = 7.36 x 10 22 kg for the Moon). 

What is the distance between the Earth and the Moon? 
www.ckl2.org 484 



Let's start with the Law of Gravitation formula. F = G 



Now plug in the known values. 
Multiply the masses together. 
Cancel the kg units. 

Multiply the numbers in the numerator. 

Multiply both sides by d 2 . 

Cancel common factors. 
Simplify. 

Divide both sides by 2.0 x 10 20 N. 

Simplify. 

Take the square root of both sides. 



m\m2 



9n u N-m 2 (5.97 xlO M kg) (7.36 xl0 22 kg) 

2.0 x W 20 N = 6.67 x 10" 11 A ' 



2.0 x 10 20 N = 6.67 x 10 



2.0 x 10 20 N = 6.67 x 10' 



kg 2 " d 2 

_ n N-m 2 4.39 xl0 47 &g 2 

kg 2 " d 2 

_ n N-m 2 4.39 xlO 47 



2.0 x W 20 N 



2.93 x 10 37 
d 2 ' 



tf 



d 2 



-N-m 2 



2.0 x 10 20 ^V • d 2 = 2 - 93> l 1Q37 • d 2 ■ N ■ m 2 



d 2 



2.0 x 10 20 N • d 2 = 2mx10 ./. N . m 2 

/ 
2.0 x 10 20 Af • d 2 = 2.93 x 10 37 N • m 2 

2 _ 2.93 x 10 37 A^ • m 2 
~ 2.0 x 10 20 N~ 
d 2 = 1.465 x 10 17 m 2 

d = 3.84 x 10 8 m 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Simplifying Rational Expressions (15:22) 



Video 



Figure 12.8: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/840 



Reduce each fraction to lowest terms. 



1 -±- 

r> X 2 -\~2x 

2 9^+3 



12x+4 



485 



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4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 



6x 2 +2x 

4x 
x-2 

x 2 -4x+4 



5x+15 

x 2 +6x+8 

x 2 +4x 

2x 2 + 10x 
x 2 + 10x+25 
x 2 +6x+5 

x 2 -x-2 

x 2 -16 
x 2 +2x-8 
3x 2 +3x-18 
2x 2 +5x-3 
x 3 +x 2 -20x 



6x 2 +6x-120 

Find the excluded values for each rational expression. 



13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 
24. 



2 

!^_ 

x+2 
2x-l 
(x-1) 2 
3x+l 
x 2 -4 

v2 



x 2 +9 

2x 2 +3x-l 

x 2 -3x-28 

5x 3 -4 

x 2 +3x 

9 
x 3 + llx 2 +30x 
4x-l 



x 2 +3x-5 
5x+ll 

3x 2 -2x-4 
x 2 -l 

2x 3 +x+3 
12 



x 2 +6x+l 

25. In an electrical circuit with resistors placed in parallel, the reciprocal of the total resistance is equal 
to the sum of the reciprocals of each resistance: ^- = ^- + ^-. If R\ = 250 and the total resistance 
is R c = 1W7, what is the resistance 7?2? 

26. Suppose that two objects attract each other with a gravitational force of 20 Newtons. If the distance 
between the two objects is doubled, what is the new force of attraction between the two objects? 

27. Suppose that two objects attract each other with a gravitational force of 36 Newtons. If the mass of 
both objects was doubled, and if the distance between the objects was doubled, then what would be 
the new force of attraction between the two objects? 

28. A sphere with radius r has a volume of |^r 3 and a surface area of 4nr 2 . Find the ratio of the surface 
area to the volume of the sphere. 

29. The side of a cube is increased by a factor of two. Find the ratio of the old volume to the new volume. 

30. The radius of a sphere is decreased by four units. Find the ratio of the old volume to the new volume. 

Mixed Review 

31. Name 4/? 6 + 7p 3 - 9. 

32. Simplify (4b 2 + b + 7b 3 ) + (5b 2 - 6b 4 + b 3 ). Write the answer in standard form. 

33. State the Zero Product Property. 

34. Why can't the Zero Product Property be used in this situation: (5jc + 1)(jc - 4) = 2? 

35. Shelly earns $4.85 an hour plus $15 in tips. Graph her possible total earnings for one day of work. 

36. Multiply and simplify: (-4x 2 + 8x - 1)(-7jc 2 + 6x + 8). 

37. A rectangle's perimeter is 65 yards. The length is 7 more yards than its width. What dimensions 
would give the largest area? 

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12.5 Multiplication and Division of Rational Ex- 
pressions 

Because a rational expression is really a fraction, two (or more) rational expressions can be combined 
through multiplication and/or division in the same manner as numerical fractions. A reminder of how to 
multiply fractions is below. 

For any rational expressions a ± 0,Z? ^ 0, c £ 0,d ^ 0, 

a c ac 

b'd = bd 
a c ad ad 

b d be be 

Example: Multiply the following j^g • |^ 
Solution: 

a 4Z? 3 4ab 3 



16b 8 5a 2 80a 2 b 8 
Simplify exponents using methods learned in chapter 8. 

4ab 3 1 





80a 2 b s 20ab 5 


Example 1: Simplify 9c 2 • ^r- 




Solution: 






4j 2 ) 9c 2 4y 2 
' 21c 4 ' 1 21c 4 




9c 2 4y 2 36cV 




1 21c 4 ~~ 21c 4 




36c 2 y 2 _ I2y 2 



21c 4 7c 2 

Multiplying Rational Expressions Involving Polynomials 

When rational expressions become complex, it is usually easier to factor and reduce them before attempt- 
ing to multiply the expressions. 

Example: Multiply ^±P • ^. 

Solution: Factor all pieces of these rational expressions and reduce before multiplying. 

4x+12 x 4(x + 3) x 



3x 2 x 2 -9 3x 2 (x + 3)(x-3) 

4(x^7 I 

3 ^ 'Xx^T(x-3) 
4 1 4 



3x x - 3 3x 2 - 9x 



Example 1: Multiply &£** • rf^g_. 



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Solution: Factor all pieces, reduce, and then multiply. 

12x 2 - x - 6 x 2 + 7x + 6 (3x + 2)(4x-3) (x+l)(x + 6) 

x 2 -l 4x 2 - 27x + 18 ~* (x+l)(x-l) (4x-3)(x-6) 

(3x + 2)X4x—^T J^KT(x + 6) 
j(ooj-tKjc - 1) 'X4j^^T(x-6) 
12x 2 -x-6 x 2 + 7x + 6 



(x 


+ l)(x 


-1) 


(3x 


■ + 2)(x 


+ 6) 


(x 


-l)(x- 


-6) 


3x 2 


+ 20x+12 



X 



2 - 1 4x 2 - 27x +18 jc 2 - 7x + 6 



Dividing Rational Expressions Involving Polynomials 

Division of rational expressions works in the same manner as multiplication. A reminder of how to divide 
fractions is below. 

For any rational expressions a^0,b^0,c^0,d^0, 

a c ad ad 
b d be be 

Example: Simplify gff - 21x2 ~ 2 *- 8 . 
Solution: 

9.x 2 - 4 21x 2 -2x-8 9jc 2 - 4 1 



2x-2 1 2x-2 21x 2 -2jc 

Repeat the process for multiplying rational expressions. 

9x 2 - 4 1 (3jc - 2)X3j^^J 



2jc-2 21x 2 -2jc-8 2(jc - 1) l&^2j(7x + 4) 

9jc 2 - 4 _ 21x 2 - 2x - 8 _ 3jc - 2 
2jc-2 1 " 14x 2 - 6jc - 8 

Real-Life Application 

Suppose Marciel is training for a running race. Marciel's speed (in miles per hour) of his training run each 
morning is given by the function x 3 - 9x, where x is the number of bowls of cereal he had for breakfast 
(1 < x < 6). Marciel's training distance (in miles), if he eats x bowls of cereal, is 3x 2 - 9x. What is the 
function for Marciel's time and how long does it take Marciel to do his training run if he eats five bowls of 
cereal on Tuesday morning? 

distance 



speed 
3x 2 - 9x 3x(x - 3) Zxfr^Sf 



time = 
time = 

time = 

x + 3 

If x = 5, then 

3 3 

time 



x 3 - 9x x{x 2 - 9) x{x + 3)Xx-^T 
3 



5 + 3 8 

Marciel will run for | of an hour. 

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Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Multiplying and Dividing Rational Expressions (9:19) 




Figure 12.9: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/841 

In 1-20, perform the indicated operation and reduce the answer to lowest terms 



1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 

22. 



2y 2 



2y 3 x 

2xy-^ 

2x 

,,2 



5x 
2v 2 



y- 

2x y 

4y 2 -l " y-3 
_y2-9 ' 2y-l 
a s b 



3b 2 



6ab 
a 2 

v-2 



x-1 ' x 2 +x-2 
33a 2 20 
-5 ' 11a 3 

2x 2 +2x-24 x 2 +x-6 



jc+4 
2 -9 



x 2 -\-3x 

3-X _;_ 

3x-5 * 2x 2 -8x-10 
x 2 -25 

x+3 
2x+l 
2x-l 



x-5 



-(x-5) 

^ 4x 2 -l 

' 1-2* 

x 2 -8x+15 

x 2 -3x 



3x^+5x-12 ^ 3x-4 
x 2 -9 ' 3x+4 

5x 2 + 16x+3 (n 2 i r v \ 
36x 2 -25 ' V DX "t- ox ; 
x 2 +7x+10 



-3x 



x 2 -9 3x 2 +4x-4 

x 2 +x-12 _j_ x^ 

x 2 +4x+4 * x+2 
x 4 -16 _^ x 2 +4 
x 2 -9 * x 2 +6x+9 
x 2 +8x+16 ^ 7x+2 



7x 2 +9x+2 ' x 2 +4x 

Maria's recipe asks for 2^ times more flour than sugar. How many cups of flour should she mix in if 
she uses 3^ cups of sugar? 

George drives from San Diego to Los Angeles. On the return trip, he increases his driving speed by 
15 miles per hour. In terms of his initial speed, by what factor is the driving time decreased on the 



489 



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return trip? 

23. Ohm's Law states that in an electrical circuit / = ^-. The total resistance for resistors placed in 
parallel is given by ^- = ■£- + ^-. Write the formula for the electric current in term of the component 
resistances: R\ and ^2- 

Mixed Review 

24. The time it takes to reach a destination varies inversely as the speed in which you travel. It takes 3.6 
hours to reach your destination traveling 65 miles per hour. How long would it take to reach your 
destination traveling 78 miles per hour? 

25. A local nursery makes two types of fall arrangements. One arrangement uses eight mums and five 
black-eyed susans. The other arrangement uses six mums and 9 black-eyed susans. The nursery can 
use no more than 144 mums and 135 black-eyed susans. The first arrangement sells for $49.99 and 
the second arrangement sells for 38.95. How many of each type should be sold to maximize revenue? 

26. Solve for r and graph the solution on a number line: -24 > |2r + 3|. 

27. What is true of any line parallel to 5x + 9y = -36? 

28. Solve for d : 3 + 5d = -d - (3x - 3). 

29. Graph and determine the domain and range: y — 9 = -x 2 - 5x. 

30. Rewrite in vertex form by completing the square. Identify the vertex: y 2 - 16y + 3 = 4. 

Quick Quiz 

1. h is inversely proportional to t. If t = -0.05153 when h = -16, find t when h = 1.45. 

2. Use f(x) = 2 ~ 5 25 for the following questions. 

(a) Find the excluded values. 

(b) Determine the vertical asymptotes. 

(c) Sketch a graph of this function. 

(d) Determine its domain and range. 

3 . Simplify 8c4+12c 4 2 - 22c+1 . 

4. Simplify 10a ^ 0a . What are its excluded values? 

5. Fill the blank with directly, inversely, or neither. "The amount of time it takes to mow the lawn 
varies with the size of the lawn mower." 

12.6 Addition and Subtraction of Rational Ex- 
pressions 

Like numerical fractions, rational expressions represent a part of a whole quantity. Remember when adding 
or subtracting fractions, the denominators must be the same. Once the denominators are identical, the 
numerators are combined by adding or subtracting like terms. 

Example 1: Simplify ^ + ^. 

Solution: The denominators are identical; therefore we can add the like terms of the numerator to simplify. 

4jc 2 - 3 2jc 2 - 1 6jc 2 - 4 

^ + T = T 

x + 5 x + 5 x-\- 5 

Not all denominators are the same however. In the case of unlike denominators, common denominators 
must be created through multiplication by finding the least common multiple. 

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The least common multiple (LCM) is the smallest number that is evenly divisible by every member 
of the set. 

What is the least common multiple of 2,4x, and Qx 2 l The smallest number 2, 4, and 6 can divide into 
evenly is six. The largest exponent of x is 2. Therefore, the LCM of 2, 4jc, and 6x 2 is 6x 2 . 

Example 2: Find the least common multiple of 2x 2 + 8x + 8 and x 3 - 4x 2 - \2x. 

Solution: Factor the polynomials completely. 

2x 2 + 8x + 8 = 2{x 2 + 4x + 4) = 2(x + 2) 2 
x 3 - 4x 2 - 12jc = jc(x 2 - 4x - 12) = jc(jc - 6)(x + 2) 

The LCM is found by taking each factor to the highest power that it appears in either expression. LCM = 

2x(x+2) 2 (x-6) 

Use this approach to add rational expressions with unlike denominators. 
Example: Add ^ " dis- 
solution: The denominators cannot be factored any further, so the LCM is just the product of the separate 
denominators. 

LCD= (jc + 2)(2jc-5) 

The first fraction needs to be multiplied by the factor (2jc-5) and the second fraction needs to be multiplied 
by the factor (x + 2). 

2 (2jc-5) 3 (jc + 2) 



x + 2 (2x-5) 2jc-5 (jc + 2) 

We combine the numerators and simplify. 

2(2x-5)-3(x + 2) _ 4x - 10 - 3x - 6 

(jc+2)(2x-5) " (x + 2)(2jc-5) 

Combine like terms in the numerator. 

jc-16 

Answer 



(x + 2)(2x-5) 

Work Problems 

These are problems where two objects work together to complete a job. Work problems often contain 
rational expressions. Typically we set up such problems by looking at the part of the task completed 
by each person or machine. The completed task is the sum of the parts of the tasks completed by each 
individual or each machine. 

Part of task completed by first person + Part of task completed by second person = One completed task 

To determine the part of the task completed by each person or machine, we use the following fact. 

Part of the task completed = rate of work x time spent on the task 

In general, it is very useful to set up a table where we can list all the known and unknown variables for 
each person or machine and then combine the parts of the task completed by each person or machine at 
the end. 

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Example: Mary can paint a house by herself in 12 hours. John can paint a house by himself in 16 hours. 
How long would it take them to paint the house if they worked together? 

Solution: Let t = the time it takes Mary and John to paint the house together. 

Since Mary takes 12 hours to paint the house by herself, in one hour she paints ^ of the house. 

Since John takes 16 hours to paint the house by himself, in one hour he paints -^ of the house. 

Mary and John work together for t hours to paint the house together. Using the formula: 

Part of the task completed = rate of work multiplied by the time spent on the task 

we can write that Mary completed -^ of the house and John completed ^ of the house in this time and 
summarize the data in the following table. 

Table 12.2: 

Painter Rate of work (per Time worked Part of Task 

hour) 



Mary 
John 



12 l 12 

16 l 16 



Using the formula: 

Part of task completed by first person + Part of task completed by second person = One completed task 

Write an equation to model the situation. 



12 16 
Solve the equation by finding the least common multiple. 

LCM = 48 
48. ± + 48-^ = 48.1 

4/ + 3/ = 48 

48 
7t = 48 => t = — = 6.86 hours Answer 

7 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Adding Rational Expressions Example 1 (3:47) 

CK-12 Basic Algebra: Adding Rational Expressions Example 2 (6:40) 

CK-12 Basic Algebra: Adding Rational Expressions Example 3 (6:23) 

Perform the indicated operation and simplify. Leave the denominator in factored form. 

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Figure 12.10: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/843 



Video 



Figure 12.11: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/844 




Figure 12.12: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/845 



493 



www.ckl2.org 



1. 



5 7_ 

24 24 



2 - 21 + 35 

Q _5 I 3_ 

°' 2x+3 ^ 2x+3 
3x-l 4x+3 



4. 

5. 
6. 



x+9 x+9 

4x+7 _ 3x-4 

2x 2 2x 2 

x 2 _ _25_ 

x+5 x+5 
7 2x _|_ x 

°- 3x-l l-3x 
y ' 2x+3 ° 

10. ^+2 

11. i + f 

* , 3x ^ 

12. 4 2 
13. 
14. 
15. 
16. 
17. 

18 - 5^+2 ~ ^~ 
10 £±i , A 
20. 5x±3 + 2£+! 
x 2 +x x 

4 



5r 2 


7x 3 


4x 


2 


x+1 


2(x+l) 


10 


^ x+2 


x+5 


2x 


3x 


x-3 


x+4 


4x-3 


, *+2 
"•" x-9 


2x+l 


x 2 


3x 2 


x+4 


4x-l 


2 


x+1 



21 ' (x+l)(x-l) (x+l)(x+2) 

22. f -g| -rr + ^ 



23. 



(x+2)(3x-4) ' (3x-4) 2 
3x+5 _ 9x-l 
x(x-l) (x-1) 2 



24 1 i 2 

Z ^' (x-2)(x-3) ^ (2x+5)(x-6) 

25. ^ + x 



27. 



2 ^ x 2 -4x+4 

rr« +x-4 

x+6 

2x 3x 



26. 2 -** + jc - 4 

x^-7x+6 



■ 2 + 10x+25 2x 2 +7x-15 
1 | 2 



28. ^.g + x 2 +5;c+6 

9Q ~*+ 4 I * 

^' 2x 2 -x-15 ^ 4x 2 +8x-5 

QQ 4 1 

ow - 9x 2 -49 3x 2 +5x-28 

31. One number is 5 less than another. The sum of their reciprocals is ||. Find the two numbers. 

32. One number is 8 times more than another. The difference in their reciprocals is ^q. Find the two 
numbers. 

33. A pipe can fill a tank full of oil in 4 hours and another pipe can empty the tank in 8 hours. If the 
valves to both pipes are open, how long would it take to fill the tank? 

34. Stefan could wash the cars by himself in 6 hours and Misha could wash the cars by himself in 5 hours. 
Stefan starts washing the cars by himself, but he needs to go to his football game after 2.5 hours. 
Misha continues the task. How long did it take Misha to finish washing the cars? 

35. Amanda and her sister Chyna are shoveling snow to clear their driveway. Amanda can clear the snow 
by herself in three hours and Chyna can clear the snow by herself in four hours. After Amanda has 
been working by herself for one hour, Chyna joins her and they finish the job together. How long 
does it take to clear the snow from the driveway? 

36. At a soda bottling plant, one bottling machine can fulfill the daily quota in ten hours and a second 
machine can fill the daily quota in 14 hours. The two machines started working together but after 
four hours the slower machine broke and the faster machine had to complete the job by itself. How 
many hours does the fast machine work by itself? 

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Mixed Review 

37. Explain the difference between these two situations. Write an equation to model each situation. 
Assume the town started with 10,000 people. When will statement b become larger than statement 
a? 

(a) For the past seven years, the population grew by 500 people every year. 

(b) For the past seven years, the population grew by 5% every year. 

38. Simplify. Your answer should have only positive exponents. _ 2 J • 2 X ~ 

39. Solve for j : -12 = j 2 - 8j. Which method did you use? Why did you choose this method? 

40. Jimmy shot a basketball from a height of four feet with an upward velocity of 12 feet/sec. 

(a) Write an equation to model this situation. 

(b) Will Jimmy's ball make it to the ten-foot-tall hoop? 

41. The distance you travel varies directly as the speed at which you drive. If you can drive 245 miles in 
five hours, how long will it take you to drive 90 miles? 

42. Two cities are 3.78 centimeters apart on an atlas. The atlas has a scale of \cm = 14 miles. What is 
the true distance between these cities? 

12.7 Solution of Rational Equations 

You are now ready to solve rational equations! There are two main methods you will learn in this lesson 
to solve rational equations: 

• Cross products 

• Lowest common denominators 

Solving a Rational Proportion 

When two rational expressions are equal, a proportion is created and can be solved using its cross 
products. For example, to solve | = 2 , cross multiply and the products are equal. 

x 0+1) 



Solve for x: 



- 2 2(x) = 5(x+l) 



2(jc) = 5(jc+1) -> 2x = 5x + 5 
2x - 5x — 5x - 5x + 5 
-3x = 5 

5 



Example 1: Solve ^- = |. 
Solution: 



2X 5 2x 2 = 5(* + 4) 



x + 4 x 



2x z = 5(jc + 4) -> 2x z = 5x + 20 



2x 2 - 5x - 20 = 



495 www.ckl2.org 



Notice that this equation has a degree of two, that is, it is a quadratic equation. We can solve it using the 
quadratic formula. 

5+ Vl85 

x = => x « -2.15 or x « 4.65 

4 

Solving by Clearing Denominators 

When a rational equation has several terms, it may not be possible to use the method of cross products. 
A second method to solve rational equations is to clear the fractions by multiplying the entire equation 
by the least common multiple of the denominators. 

Example: Solve ^ - ^ = ^ZTq- 

Solution: Factor all denominators and find the least common multiple. 



x + 2 x-5 (x + 2)(x-5) 
LCM = (x + 2)(x-5) 

Multiply all terms in the equation by the LCM and cancel the common terms. 

(x + 2)(x - 5) • — (x + 2)(x - 5) = (x + 2)(x - 5) • 2 



x + 2 x-5 (x + 2)(x-5) 



Now solve and simplify. 



Check your answer. 



jH-^ j^5 ^^ yv J (jiJ^frc^f 



3(x-5)-4(x + 2) = 2 
3x-15-4x-8 = 2 

x = -25 Answer 



= 0.003 



x + 2 x-5 -25 + 2 -25-5 
2 _ 2 

x 2 - 3x - 10 " (-25) 2 -3(-25)-10 " °*° 03 

Example: A group of friends decided to pool their money together and buy a birthday gift that cost $200. 
Later 12 of the friends decided not to participate any more. This meant that each person paid $15 more 
than the original share. How many people were in the group to start? 

Solution: Let x = the number of friends in the original group 

Table 12.3: 

Number of People Gift Price Share Amount 



Original group x 200 

Later group x - 12 200 



200 

jbo 

jc-12 



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Since each person's share went up by $15 after 2 people refused to pay, we write the equation: 

200 200 



+ 15 



jt-12 

Solve by clearing the fractions. Don't forget to check! 

LCM = x(x - 12) 
x(x - 12) • — — - = x(x - 12) • — + x(x - 12) • 15 

xjx^m- -^?- = i[x - 12) ~ + x(x - 12) • 15 

200x = 200O - 12) + 15jc(jc - 12) 
200x = 200x - 2400 + 15x 2 - 180x 

= 15x 2 - 180x - 2400 

x = 20,x = -8 

The answer is 20 people. We discard the negative solution since it does not make sense in the context of 
this problem. 



Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following videos. 
Note that there is not always a match between the number of the practice exercise in the videos and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Solving Rational Equations (12:57) 




Figure 12.13: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/846 

CK-12 Basic Algebra: Two More Examples of Solving Rational Equations (9:58) 
Solve the following equations. 



1. 
2. 
3. 

4. 
5. 

6. 



2jc+1 


jc— 3 


4 " 


" 10 


Ax 


5 


jc+2 


9 


5 


2 


3jc-4 ~ 


x+1 


7x 


x+3 


x f 


i 


x+3 


x+4 


3x 2 +2.x 


-1 __ 




-2 



497 



www.ckl2.org 




Figure 12.14: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view/847 



7. x+± = 2 

8. -3 + -|r = 



9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 



JC+1 

1 X_ _ € 

x x-2 

__3 i _J2_ 

2x-l "•" x+4 
2x x 

x-1 



= 2 
= 3 



x+1 
x-1 



+ 



-JL_ J 

x-2 ~ x+3 



x 2 +4x+3 

_J 1_ 

x+5 x-5 



3x+4 
x-4 _ o 
x+4 — ° 
x 



1 



x z -\-x- 



2 + 



-36 



2x 



+ x-6 ~~ 
1 _ 



3x+3 

— + 

x-2 ^ 



4x+4 
3x-l _ 

x+4 



x-2 

x+3 
1-x 
x+5 
1 
x+6 

2 

x+1 
1 



c 2 +2x-8 

19. Juan jogs a certain distance and then walks a certain distance. When he jogs he averages seven miles 
per hour. When he walks, he averages 3.5 miles per hour. If he walks and jogs a total of six miles in 
a total of seven hours, how far does he jog and how far does he walk? 

20. A boat travels 60 miles downstream in the same time as it takes it to travel 40 miles upstream. The 
boat's speed in still water is 20 miles/hour. Find the speed of the current. 

21. Paul leaves San Diego driving at 50 miles/hour. Two hours later, his mother realizes that he forgot 
something and drives in the same direction at 70 miles/hour. How long does it take her to catch up 
to Paul? 

22. On a trip, an airplane flies at a steady speed against the wind. On the return trip the airplane flies 
with the wind. The airplane takes the same amount of time to fly 300 miles against the wind as it 
takes to fly 420 miles with the wind. The wind is blowing at 30 miles/hour. What is the speed of 
the airplane when there is no wind? 

23. A debt of $420 is shared equally by a group of friends. When five of the friends decide not to pay, 
the share of the other friends goes up by $25. How many friends were in the group originally? 

24. A non-profit organization collected $2,250 in equal donations from their members to share the cost 
of improving a park. If there were thirty more members, then each member could contribute $20 
less. How many members does this organization have? 



Mixed Review 



25. Divide -2^--f . 

26. Solve for g : -1.5 (-3§ + #) = fp 

27. Find the discriminant of 6x 2 + 3x + 4 = and determine the nature of the roots. 



6b 



28. Simplify 2b+2 

29. Simplify ^ 



+ 3. 

_ 5x 
x-5' 



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498 



30. Divide (7x 2 + 16* - 10) * (jc + 3). 

31. Simplify (n - 1) * (3n + 2)(n - 4). 

12.8 Surveys and Samples 

One of the most important applications of statistics is collecting information. Statistical studies are done 
for many purposes: 

• To find out more about animal behaviors; 

• To determine which presidential candidate is favored; 

• To figure out what type of chip product is most popular; 

• To determine the gas consumption of cars. 

In most cases except the Census, it is not possible to survey everyone in the population. So a sample is 
taken. It is essential that the sample is a representative sample of the population being studied. For 
example, if we are trying to determine the effect of a drug on teenage girls, it would make no sense to 
include males in our sample population, nor would it make sense to include women that are not teenagers. 

The two types of sampling methods studied in this book are: 

• Random Sampling 

• Stratified Sampling 

Random Samples 

Random sampling is a method in which people are chosen "out of the blue." In a true random sample, 
everyone in the population must have the same chance of being chosen. It is important that each person 
in the population has a chance of being picked. 

Stratified Samples 

Stratified sampling is a method actively seeking to poll people from many different backgrounds. The 
population is first divided into different categories (or strata) and the number of members in each category 
is determined. 

Sample Size 

In order to lessen the chance of a biased result, the sample size must be large enough. The larger the 
sample size is, the more precise the estimate is. However, the larger the sample size, the more expensive 
and time-consuming the statistical study becomes. 

Example 1: For a class assignment you have been asked to find if students in your school are planning 
to attend university after graduating high school. Students can respond with "yes," "no," or "undecided." 
How will you choose those you wish to interview if you want your results to be reliable? 

Solution: 

The stratified sampling method would be the best option. By randomly picking a certain number of 
students in each grade, you will get the most accurate results. 

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Biased Samples 

If the sample ends up with one or more sub-groups that are either over- represented or under- represented, 
then we say the sample is biased. We would not expect the results of a biased sample to represent the 
entire population, so it is important to avoid selecting a biased sample. 

Some samples may deliberately seek a biased sample in order to obtain a particular viewpoint. For example, 
if a group of students were trying to petition the school to allow eating candy in the classroom, they might 
only survey students immediately before lunchtime when students are hungry. The practice of polling only 
those who you believe will support your cause is sometimes referred to as cherry picking. 

Many surveys may have a non-response bias. In this case, a survey that is simply handed out gains 
few responses when compared to the number of surveys given out. People who are either too busy or 
simply not interested will be excluded from the results. Non-response bias may be reduced by conducting 
face-to-face interviews. 

Self-selected respondents who tend to have stronger opinions on subjects than others and are more 
motivated to respond may also cause bias. For this reason phone-in and online polls also tend to be poor 
representations of the overall population. Even though it appears that both sides are responding, the 
poll may disproportionately represent extreme viewpoints from both sides, while ignoring more moderate 
opinions that may, in fact, be the majority view. Self-selected polls are generally regarded as unscientific. 

Example 2: Determine whether the following survey is biased. Explain your reasoning. 

"Asking people shopping at a farmer's market if they think locally grown fruit and vegetables are healthier 
than supermarket fruits and vegetables" 

Solution: This would be a biased sample because people shopping a farmer's market are generally in- 
terested in buying fresher fruits and vegetables than a regular supermarket provides. The study can be 
improved by interviewing an equal number of people coming out of a supermarket, or by interviewing 
people in a more neutral environment such as the post office. 



Biased Questions 

Although your sample may be a good representation of the population, the way questions are worded in 
the survey can still provoke a biased result. There are several ways to identify biased questions. 



1. They may use polarizing language, words, and phrases that people associate with emotions. 

(a) How much of your time do you waste on TV every week? 

2. They may refer to a majority or to a supposed authority. 

(a) Would you agree with the American Heart and Lung Association that smoking is bad for your 
health? 

3. They may be phrased so as to suggest the person asking the question already knows the answer to 
be true, or to be false. 

(a) You wouldn't want criminals free to roam the streets, would you? 

4. They may be phrased in an ambiguous way (often with double negatives), which may confuse people. 

(a) Do you disagree with people who oppose the ban on smoking in public places? 

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Design and Conduct a Survey 

The method in which you design and conduct the survey is crucial to its accuracy. Surveys are a set of 
questions in which the sample answers. The data is compiled to form results, or findings. When designing 
a survey, be aware of the following recommendations. 

1. Determine the goal of your survey. What question do you want to answer? 

2. Identify the sample population. Who will you interview? 

3. Choose an interviewing method, face-to-face interview, phone interview, or self-administered paper 
survey or internet survey. 

4. Conduct the interview and collect the information. 

5. Analyze the results by making graphs and drawing conclusions. 

Surveys can be conducted in several ways. 
Face-to-face interviews 

y Fewer misunderstood questions 

y High response rate 

y Additional information can be collected from respondents 

• Time-consuming 

• Expensive 

• Can be biased based upon the attitude or appearance of the surveyor 

Self-administered surveys 

y Respondent can complete on their free time 
y Less expensive than face-to-face interviews 
y Anonymity causes more honest results 

• Lower response rate 

Example: Martha wants to construct a survey that shows which sports students at her school like to play 
the most. 

1. List the goal of the survey. 

2. What population sample should she interview? 

3. How should she administer the survey? 

4. Create a data collection sheet that she can use to record her results. 

Solution: The goal of the survey is to find the answer to the question: "Which sports do students at 
Martha's school like to play the most?" 

1. A sample of the population would include a random sample of the student population in Martha's 
school. A good stategy would be to randomly select students (using dice or a random number 
generator) as they walk into an all-school assembly. 

2. Face-to-face interviews are a good choice in this case since the survey consists of only one question, 
which can be quickly answered and recorded. 

3. In order to collect the data to this simple survey, Martha can design a data collection sheet such as 
the one below: 



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Table 12.4: 



Sport 



Tally 



baseball 

basketball 

football 

soccer 

volleyball 

swimming 



Display, Analyze, and Interpret Survey Data 

This textbook has shown you several ways to display data. These graphs are also useful when displaying 
survey results. Survey data can be displayed as: 

• A bar graph 

• A histogram 

• A pie chart 

• A tally sheet 

• A box-and-whisker plot 

• A stem-and-leaf plot 

The method in which you choose to display your data will depend upon your survey results and to whom 
you plan to present the data. 

Practice Set 

Sample explanations for some of the practice exercises below are available by viewing the following video. 
Note that there is not always a match between the number of the practice exercise in the video and the 
number of the practice exercise listed in the following exercise set. However, the practice exercise is the 
same in both. 

CK-12 Basic Algebra: Surveys and Samples (12:09) 




Figure 12.15: (Watch Youtube Video) 

http://www.ckl2.org/flexbook/embed/view 



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502 



1. Explain the most common types of sampling methods. If you needed to survey a city about a new 
road project, which sampling method would you choose? Explain. 

2. What is a biased survey! How can bias be avoided? 

3. How are surveys conducted, according to this text? List one advantage and one disadvantage of 
each? List one additional method that can be used to conduct surveys. 

4. What are some keys to recognizing biased questions? What could you do if you were presented with 
a biased question? 

5. For a class assignment, you have been asked to find out how students get to school. Do they take 
public transportation, drive themselves, have their parents drive them, use carpool, or walk/bike. 
You decide to interview a sample of students. How will you choose those you wish to interview if you 
want your results to be reliable? 

6. Comment on the way the following samples have been chosen. For the unsatisfactory cases, suggest 
a way to improve the sample choice. 

(a) You want to find whether wealthier people have more nutritious diets by interviewing people 
coming out of a five-star restaurant. 

(b) You want to find if a pedestrian crossing is needed at a certain intersection by interviewing 
people walking by that intersection. 

(c) You want to find out if women talk more than men by interviewing an equal number of men 
and women. 

(d) You want to find whether students in your school get too much homework by interviewing a 
stratified sample of students from each grade level. 

(e) You want to find out whether there should be more public busses running during rush hour by 
interviewing people getting off the bus. 

(f) You want to find out whether children should be allowed to listen to music while doing their 
homework by interviewing a stratified sample of male and female students in your school. 

7. Raoul wants to construct a survey that shows how many hours per week the average student at his 
school works. 

(a) List the goal of the survey. 

(b) What population sample will he interview? 

(c) How would he administer the survey? 

(d) Create a data collection sheet that Raoul can use to record his results. 

8. Raoul found that 30% of the students at his school are in 9 th grade, 26% of the students are in the 
10* grade, 24% of the students are in 11* grade, and 20% of the students are in the 12* grade. 
He surveyed a total of 60 students using these proportions as a guide for the number of students he 
interviewed from each grade. Raoul recorded the following data. 

Table 12.5: 

Grade Level Record Number of Hours Total Number of Students 

Worked 

9* grade 0, 5, 4, 0, 0, 10, 5, 6, 0, 0, 2, 4, 0, 18 

8, 0, 5, 7, 
10* grade 6, 10, 12, 0, 10, 15, 0, 0, 8, 5, 0, 16 

7, 10, 12, 0, 
11* grade 0, 12, 15, 18, 10, 0, 0, 20, 8, 15, 14 

10, 15, 0, 5 
12* grade 22, 15, 12, 15, 10, 0, 18, 20, 10, 12 

0, 12, 16 

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(a) Construct a stem-and-leaf plot of the collected data. 

(b) Construct a frequency table with bin size of 5. 

(c) Draw a histogram of the data. 

(d) Find the five-number summary of the data and draw a box-and- whisker plot. 

9. The following pie chart displays data from a survey asking students the type of sports they enjoyed 
playing most. Make five conclusions regarding the survey results. 

fencing 

gymnastics 



swimming 
7°/c " 



3% 2 ° /o 



volleyball 
8% 




10. Melissa conducted a survey to answer the question: "What sport do high school students like to 
watch on TV the most?" She collected the following information on her data collection sheet. 

Table 12.6: 

Sport Tally 

Baseball mm mm mm mm mm mm i . 32 

rttl iTH rm ittI rttl rm II 

Basketball 28 



JJJJ LLIJ LLLI LL1J LLU 

mhmMmrfflr 
rttl rttl rttl rttl 

HUH III 



Football LLU LLU U4-I UUU I 24 

rttl rttl rttl rttl INI 

S ° CCer LLU LLLJ LLU 1 1 1 18 

Gymnastics 19 

Figure Skating 

Hockey 18 



Km mirfH III 

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Table 12.6: (continued) 



Sport 



Tally 



Total 147 



(a) Make a pie chart of the results showing the percentage of people in each category. 

(b) Make a bar- graph of the results. 

11. Samuel conducted a survey to answer the following question: "What is the favorite kind of pie of 
the people living in my town?" By standing in front of his grocery store, he collected the following 
information on his data collection sheet: 

Table 12.7: 



Type of Pie 



Tally 



Apple 
Pumpkin 
Lemon Meringue 
Chocolate Mousse 
Cherry 

Chicken Pot Pie 
Other 



jjlu mj mi jjjj mi IWJLWfl 
mi ml ml ml ml ml rm 

Mill 
HUH 

HH HUM III 23 



MM Liil LLU LLLI LLU LMJ 

rtti rttl rm rm rm rttl 

HU 



31 



Total 122 



(a) Make a pie chart of the results showing the percentage of people in each category. 

(b) Make a bar graph of the results. 

12. Myra conducted a survey of people at her school to see "In which month does a person's birthday 
fall?" She collected the following information in her data collection sheet: 

Table 12.8: 
Month Tally 



January 



ml rttl ml 



16 



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Table 12.8: (continued) 



Month 



Tally 



February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

December 



MM LLM 

rttlrttl 

MM MM 

rttlrttl 

LLM MM 

rttlrttl 

MM MM 

rttlrttl 

MM LLU 

rttlrttl 



MM 

MM 



m 



Hill 



13 
12 
11 
13 
12 



13 
13 
Total: 136 



(a) Make a pie chart of the results showing the percentage of people whose birthday falls in each month. 

(b) Make a bar graph of the results. 

13. Nam-Ling conducted a survey that answers the question: "Which student would you vote for in your 
school's elections?" She collected the following information: 

Table 12.9: 



Candidate 



9 graders 



10 f/z graders ll ?/z graders 12 f/z graders Total 



Susan Cho 

Margarita 
Martinez 

Steve Coogan 
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rttlrttl 

WJIW 
rttlrttl 

IMJ LLU 

rttlrttl 



llll LLU 

rttlrttl 

WJIW 
rttlrttl 

LLM Mil 

rttlrttl 



rttlrttl 
rttlrttl 



rttlrttl 



19 



31 



16 



506 



Table 12.9: (continued) 



Candidate 9 graders 10 graders 11 graders 12 graders 



Solomon Dun- 
ing 

Juan Rios 
Total 



IJJJ LMJ 

rttlrttl 

LLM LMJ 

rttlrttl 



MM LMJ Mil LLM 

Irtti rttlrttl 

MM LMJ LLM 

rtti rttlrttl 



MU MM 

rttlrttl 
rttlrttl 



36 



30 



30 



24 



Total 

26 

28 
120 



(a) Make a pie chart of the results showing the percentage of people planning to vote for each candidate. 

(b) Make a bar graph of the results. 

14. Graham conducted a survey to find how many hours of TV teenagers watch each week in the United 
States. He collaborated with three friends who lived in different parts of the U.S. and found the 
following information: 



Table 12.10: 



Part of the country 



Number of hours of TV Total number of teens 
watched per week 



West Coast 
Mid West 

New England 

South 



10, 12, 8, 20, 6, 0, 15, 18, 12, 22, 20 

9, 5, 16, 12, 10, 18, 10, 20, 24, 8 

20, 12, 24, 10, 8, 26, 34, 15, 18, 20 

6, 22, 16, 10, 20, 15, 25, 32, 12, 

18, 22 

16, 9, 12, 0, 6, 10, 15, 24, 20, 30, 20 

15, 10, 12, 8, 28, 32, 24, 12, 10, 

10 

24, 22, 12, 32, 30, 20, 25, 15, 10, 20 

14, 10, 12, 24, 28, 32, 38, 20, 25, 

15, 12 



(a) Make a stem-and-leaf plot of the data. 

(b) Decide on an appropriate bin size and construct a frequency table. 

(c) Make a histogram of the results. 

(d) Find the five-number summary of the data and construct a box-and-whisker plot. 

15. "What do students in your high school like to spend their money on?" 

(a) Which categories would you include on your data collection sheet? 

(b) Design the data collection sheet that can be used to collect this information. 

(c) Conduct the survey. This activity is best done as a group with each person contributing at least 
20 results. 

(d) Make a pie chart of the results showing the percentage of people in each category. 

(e) Make a bar graph of the results. 



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16. "What is the height of students in your class?" 

(a) Design the data collection sheet that can be used to collect this information. 

(b) Conduct the survey. This activity is best done as a group with each person contributing at least 
20 results. 

(c) Make a stem-and-leaf plot of the data. 

(d) Decide on an appropriate bin size and construct a frequency table. 

(e) Make a histogram of the results. 

(f) Find the five- number summary of the data and construct a box- and- whisker plot. 

17. "How much allowance money do students in your school get per week?" 

(a) Design the data collection sheet that can be used to collect this information. 

(b) Conduct the survey. This activity is best done as a group with each person contributing at least 
20 results. 

(c) Make a stem-and-leaf plot of the data. 

(d) Decide on an appropriate bin size and construct a frequency table. 

(e) Make a histogram of the results. 

(f) Find the five- number summary of the data and construct a box- and- whisker plot. 

18. Are the following statements biased? 

(a) You want to find out public opinion on whether teachers get paid a sufficient salary by inter- 
viewing the teachers in your school. 

(b) You want to find out if your school needs to improve its communications with parents by sending 
home a survey written in English. 

19. "What time do students in your school get up in the morning during the school week?" 

(a) Design the data collection sheet that can be used to collect this information. 

(b) Conduct the survey. This activity is best done as a group with each person contributing at least 
20 results. 

(c) Make a stem-and-leaf plot of the data. 

(d) Decide on an appropriate bin size and construct a frequency table. 

(e) Make a histogram of the results. 

(f) Find the five- number summary of the data and construct a box- and- whisker plot. 

Mixed Review 

20. Write the equation containing (8, 1) and (4, -6) in point-slope form. 

(a) What is the equation for the line perpendicular to this containing (0, 0)? 

(b) What is the equation for the line parallel to this containing (4, 0)? 

21. Classify v64 according to the real number hierarchy. 

22. A ferry traveled to its destination, 22 miles across the harbor. On the first voyage, the ferry took 
45 minutes. On the return trip, the ferry encountered a head wind and its trip took one hour, ten 
minutes. Find the speed of the ferry and the speed of the wind. 

23. Solve for a: ^ = -^. 

24. Simplify ^ §f. " 

25. Use long division to simplify: ^^X^w-so^ - 

26. A hot air balloon rises 16 meters every second. 

(a) Is this an example of a linear function, a quadratic function, or an exponential function? Explain. 

(b) At four seconds the balloon is 68.5 meters from the ground. What was its beginning height? 

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12.9 Chapter 12 Review 

Define the following terms used in this chapter. 

1. Inverse variation 

2. Asymptotes 

3. Hyperbola 

4. Points of discontinuity 

5. Least common multiple 

6. Random sampling 

7. Stratified sampling 

8. Biased 

9. Cherry picking 

10. What quadrants are the branches of the hyperbola located if k < 0? 

Are the following examples of direct variation or inverse variation? 

11. The number of slices n people get from sharing one pizza 

12. The thickness of a phone book given n telephone numbers 

13. The amount of coffee n people receive from a single pot 

14. The total cost of pears given the nectarines cost $0.99 per pound 

For each variation equation: 

1. Translate the sentence into an inverse variation equation. 

2. Find k, the constant of variation. 

3. Find the unknown value. 

15. y varies inversely as x. When x = 5, v = ^. Find y when x = -^. 

16. y is inversely proportional to the square root of y. When x = 16, y = 0.5625. Find y when x = |. 

17. Habitat for Humanity uses volunteers to build houses. The number of days it takes to build a 
house varies inversely as the number of volunteers. It takes eight days to build a house with twenty 
volunteers. How many days will it take sixteen volunteers to complete the same job? 

18. The Law of the Fulcrum states the distance you sit to balance a seesaw varies inversely as your 
weight. If Gary weighs 20.43 kg and sits 1.8 meters from the fulcrum, how far would Shelley sit, 
assuming she weighs 36.32 kilograms? 

For each function: 

1. Graph it on a Cartesian plane. 

2. State its domain and range. 

3. Determine any horizontal and/or vertical asymptotes the function may have. 



19. 


y= * 


20. 


/to - 4^ 


21. 


£to = I+T 


22. 


?=3*+l 2 


23. 


/to = |-5 



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Perform the indicated operation. 

9/1 5<z 5£ 

25- £ + % 
26. & + * 



2x;y ' 3 

x+5 



5n-2 ' 2 

2x+l 



27. ^_ + 2n 

28. 

29. 

30. 



3x+9 3x+9 
5m+/i _ 4m+/i 

30rc 4 30rc 4 

r-6 r+6 



4r 2 -12r+8 4r 2 -12r+8 
Q1 2 , x-2y 



16x 3 ;y 2 16x 3 y 
qq n-6 j_ 2rc 



,2 



33. 



x+5 

4 x+8 

°*' 2(x+l) ^ 7x-6 
11 20x 2 
8 ' 2 
17r 7r 4 



35. 
36. 
37. 

38. 
39. 
40. 
41. 

42. 
43. 
44. 
45. 



16 16 

15 JA 

18 ' 17/ 

2(6-11) fr+5 

14/? ' (fc+5)(fc-ll) 

17w 2 18(w+4) 
w+4 ' 17w 2 (w-9) 
10.y 3 -3Q^ 2 j-3 
30s 2 -10s 3 ' 8 

1 j_ /+3 
/-5 * / 2 +6/+9 
Q+8)Q+3) ^ 10fl 2 (>+10) 
4(a+3) ' 4 

1 ^ (/i-4) 

(/*-10)(/i+7) * 4h(h-10) 

2(5x-8) ^ _6_ 
4x 2 (8-5x) * 4x 2 

2(g-7) . 1 

40g(g+l) ' 40g(g+l) 



Solve each equation. 



46 A-IjlJ_ 
4D - 3x 2 _ x + 3x 2 



47. 

48. 
49. 



2 _ 12 
5x 2 ~~ x-3 

7x _ 3 



x-6 4x+16 
4 _J_ 

c-2 c+4 



0U - 4J 2 - 4J 2 + 4J 

1 _ 2z-12 _ z+1 

2 ~ z Az 



51. 

52. 1 = ^ + fi 

W I--L + I 

0<3 * 2a — 2« 2 + a 

r^ £+4 _ 5fc-30 , J_ 

04 ' £ 2 _ 3£ 2 ^ 3£ 2 

55. It takes Jayden seven hours to paint a room. Andie can do it in five hours. How long will it take to 
paint the room if Jayden and Andie work together? 

56. Kiefer can mow the lawn in 4.5 hours. Brad can do it in two hours. How long will it take if they 
worked together? 

57. Melissa can mop the floor in 1.75 hours. With Brad's help, it took only 50 minutes. How long would 
it take Brad to mop it alone? 

58. Working together, it took Frankie and Ricky eight hours to frame a room. It would take Frankie 
fifteen hours doing it alone. How long would it take Ricky to do it alone? 

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59. A parallel circuit has R± = 500 and R t = 160. Find R2- 

60. A parallel circuit has R\ = 60 and R2 = 90. Fmd 7?^. 

61. A series circuit has 7?i = 2000 and R t = 3000. Find R2- 

62. A series circuit has R\ = 110 and R2 = 250. Fmd Rt- 

63. Write the formula for the total resistance for a parallel circuit with three individual resistors. 

64. What would be the bias in this situation? To determine the popularity of a new snack chip, a survey 
is conducted by asking 75 people walking down the chip aisle in a supermarket which chip they prefer. 

65. Describe the steps necessary to design and conduct a survey. 

66. You need to survey potential voters for an upcoming school board election. Design a survey with at 
least three questions you could ask. How will you plan to conduct the survey? 

67. What is a stratified sampled Name one case where a stratified sample would be more beneficial. 



12.10 Chapter 12 Test 



1. True or false? A horizontal asymptote has the equation y = c and represents where the denominator 
of the rational function is equal to zero. 

2. A group of SADD members want to find out about teenage drinking. They conduct face-to- face 
interviews, wearing their SADD club shirts. What is a potential bias? How can this be modified to 
provide accurate results? 

3. Name the four types of ways questions can be biased. 

4. Which is the best way to show data comparing two categories? 

5. Consider f(x) = --. State its domain, range, asymptotes, and the locations of its branches. 

6. h varies inversly as r. When h = -2.25, r = 0.125. Find h when r = 12. 

7. Name two types of visual displays that could be used with a frequency distribution. 

8. Tyler conducted a survey asking the number of pets his classmates owned and received the following 
results: 0, 2, 1, 4, 3, 2, 1, 0, 0, 0, 0, 1, 4, 3, 2, 3, 4, 3, 2, 1, 1, 1, 5, 7, 0, 1, 2, 3, 2, 1, 4, 3, 2, 1, 1, 

(a) Display this data a frequency distribution chart. 

(b) Use it to make a histogram. 

(c) Find its five-number summary. 

(d) Draw a box- and- whisker plot. 

(e) Make at least two conclusions regarding Tyler's survey. 

9. Find the excluded values, the domain, the range, and the asymptotes of: 






Perform the indicated operation. 



10 _j_ , 4r+5f 

iU ' 21r 4 + 21r 4 

1 1 a ~ v _ a+5v 

11 ' 12a 3 12a 3 

12 -§- + ^ 

10 _4£_ 1 24 

10 ' 5f-8 - 1 " 12 

4 _80_ 

5 ' 48m 

1 . J+7 



d-8 ' 2J+14 

1 j_ u-4 
u-3 ' 2u-6 



14. 

15. 

16 - i 
Solve. 



1 7 7w 7w 

' ' w-7 ~ w+5 



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18. 


p-6 7 
3p 2 -6p 3 


19. 


2 1 jc+1 


x 2 ~ 2x 2 2x 2 


20. 


1 1 3 


2 4r — 4 


21. 


y-5 _ iii 

3y 2 ~ Sy^y 2 



22. Working together, Ashton and Matt can tile a floor in 25 minutes. Working alone, it would take 
Ashton two hours. How long would it take Matt to tile the floor alone? 

23. Bethany can paint the deck in twelve hours. Melissa can paint the deck in five hours. How long 
would it take the girls to paint the deck, working together? 

24. A parallel circuit has R t = 115 Q and R2 = 75 ft. Find R\. 

25. A series circuit has R\ = 13 ft and R t = 21 17. Find R2. 

Texas Instruments Resources 

In the CK-12 Texas Instruments Algebra I FlexBook, there are graphing calculator activities 
designed to supplement the objectives for some of the lessons in this chapter. See http: 
//www. ckl2. org/flexr/chapter/9622. 



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